In reply to MM0FMF:
There are abbreviated forms of eight of the ten numerical digits in Morse Code.
0 = dah
1 = dit dah
2 = dit dit dah
3 = dit dit dit dah
5 = dit
7 = dah dit dit dit
8 = dah dit dit
9 = dah dit
In practice, the only ones I have ever heard used on the amateur bands are
0, 1, 5 and 9. These can quite often be heard in CW contests. Abbreviated numbers should never be used in callsigns … it would be a recipe for total confusion!
… … de G3NYY