Another thread ( Definition of a valid SOTA QSO) indicates rules are under review.
I’ll offer some thoughts:
The exchange includes a signal report. I generally use a 5w HT with no meters and a basic situation that I have a signal or I don’t and will give a LOUD AND CLEAR. Sometimes I will state “you’re down in the noise”. Sometimes I’ll give a 59. You may be a 36 but I have no way of knowing and a 59 may be misleading. My experience suggests that an automatic 59 is that’s reserved for contesting when the object is to save time and get out of the way for the next contact. Yes, it works here to, but the objective of SOTA is to get an understanding of your radio. Some operators seem to reject the LOUD AND CLEAR and seem insistent on numbers. Fill them in your self.
If the signal exchange is to be maintained, LOUD AND CLEAR shoul be noted as an acceptable response.
What makes you think it isn’t already acceptable?
Agreed, that exchange is fine already - and also if you have no meter and NEED a number for logging or whatever than a 5x report is totally valid. Do what you can. If you can hear them and there’s no noise that’s a readability 5.
Edit: People say you should infer S from what you hear (R) - I absolutely disagree and would only give a reading if I had a measured one. Sometimes I say “you are 5 9 but I can only be sure of the 5” and leave it at that.
reports are always subjective. well i have been giving them for almost 70 years
what some folks can read (R) varies. no two ops are the same
R stands for “Readability”. Readability is a qualitative assessment of how easy or difficult it is to correctly copy the information being sent during the transmission. In a Morse code telegraphy transmission, readability refers to how easy or difficult it is to distinguish each of the characters in the text of the message being sent; in a voice transmission, readability refers to how easy or difficult it is for each spoken word to be understood correctly. Readability is measured on a scale of 1 to 5.[8]
- Unreadable
- Barely readable, occasional words distinguishable
- Readable with considerable difficulty
- Readable with practically no difficulty
- Perfectly readable
And it is helpful to know what sort of strength your signal might be with the station you are working, whether that is based on an S meter reading or the operator’s subjective interpretation of the reporting system. If all I have to go on is “loud and clear”, then it would have to go into my log as 59 and it may therefore be as meaningless as a contest report.
There’s always 2 ways of looking at things.
Except in Blackadder’s “Spanish Inquisition” sketch 
I’ve clearly spent way too much time with my FT-817 - nine times out of ten I tell what the S meter is saying based on what I’m hearing.
I think a L&C is acceptable. It’s operators who repeatedly ask for a signal report after I’ve told them L&C two or three times.
Victor KI7MMZ
Try C&L at least it would be consistent with RS 
Well just to put the cat among the pigeons 
Coming from a DXing, DXpeditioning & Contesting background I am only interested in putting as many stations in the log from the summit in the time available as possible. I don’t need to test/learn my radio, I would not have hauled it all the way up there unless I was sure it would do the job. I do try rather than actively test different antennas but that’s by gut feeling of how I’m getting out and what the band feels like. Therefore if I can hear you and you are from your home station you are getting a 5NN, if you are /P or /M you are getting a 55N. As for received reports, I might mentally note if a station sends me a particularly good report or if the majority of callers are giving poor reports (and consider why). Meter readings are meaningless, as they vary not only across rigs but also across bands on a particular rig, and of course many SOTA radios don’t feature a meter at all.
All I need to be sure of is that the other station and I have had an exchange, I would be just as happy if I sent " DL1ABC GM" and he replied with " TU GM" but, we need numbers so 5NN will do just fine 
what can I tell ya, I just love rate
73
Dec
ei6fr
The military don’t have a problem with that kind of report.
As well as the readability (R) the signal strength (S) can be assessed qualitatively by the human operator in the absence of an S-meter. We may not be able to grade it accurately to nine different levels S1-S9, but we can surely distinguish between faint, weak, fair, good, strong and very strong, and state the perceived strength in words or to the appropriate S number.
I disagree with those who say it must come from a meter reading. Given all the variables that affect the transmission path and the receiver, I question how being given an S7 or S8 makes any real difference.
I would take “clear” to be R5 and “loud” to be S8-S9.
Meter readings are usually meaningless. Are you sure your rig’s meter is correctly calibrated? It should be 6dB per S unit but they rarely are.
On 2m FM my SOTA chasers often don’t give a 59 or whatever, but I know they can hear me just fine from what they say to me.
For those who think “loud and clear” doesn’t count, they should take part in Exercise Blue Ham when you can contact air cadets on 60m. Sending a 59 will totally confuse them as they are taught “loud and clear” and such like.
Should my signal report be given with the preamp switched on or off?
Yes.
After all is said and done, ANY report is OK. If I had to rely on my
S-meter and used that to give reports, about 90 percent of the SOTA
activators would be S-zero. I went years with old receivers with no
meter. In that case you give out whatever you feel is right, I don’t
think most ops really care what the report is as long as they could
copy it and the QSO is made.
If you have to turn the preamp on to copy them, they must be pretty
weak!
73
John, K6YK
Chaser: “You’re loud and clear”.
Me: “QSL, I’ll put that down as a 59”.
No rule change necessary.
Ding! Ding! Ding! We have a winner! Spot on John. You have a to give “a report”, the format is not specified.
The only operation I can think of that has an actual minimum report
is the USA-CA (USA County Award) County Hunter’s net. 2 X 2 or
229 is the minimum. Don’t ask me why but that’s their rule for as
long as I can remember. I give out a lot of 229s on SOTA contacts
meaning “if you were any weaker I couldn’t hear you at all!”
73
John, K6YK
I never look at the s-meter on my activations…all reports are based on what I hear and I then make a guess as to the report I send.
For me saying “your 55” is faster and simpler than anything else…a longer report may be lost in the QSB that QRP signals are prone to…plus it’s what the other station is expecting to hear.
Pete
WA7JTM