The ARRL Ham Radio License Manual (2014) seems to concur:
"Self-Assigned Indicators
When operating away from your home station, you should add information to your call sign so that
other stations are aware of your location. For example, an Alaskan station would add some extra
information when operating in the lower 48 contiguous states. Otherwise, the special Alaskan
prefixes (AL7, KL7, NL7, WL7) would cause confusion about the location of the station. For
example, if KL7CC is operating from a location in the 3rd district, he could give his call sign as
“KL7CC/W3.” The added “/W3” is called a self-assigned indicator.
FCC Part 97.119© says, “One or more indicators may be included with the call sign. Each
indicator must be separated from the call sign by the slant mark (/) or by any suitable word that
denotes the slant mark. If an indicator is self-assigned, it must be included before, after, or both
before and after, the call sign.” For example, on phone, KL7CC could identify as W3/KL7CC or
KL7CC/W3, using “stroke,” “slash” or “portable” between the indicator and the call sign. [T1F06]
Note that the indicator is not allowed to conflict with some other indicator specified in the FCC
rules, such as those that indicate an upgraded license class as in the next section. It may not conflict
with a prefix assigned to some other country. For example, the indicator /M to indicate mobile
operation is not allowed because M is an English prefix, but /MOB is permitted because MOB is not
a prefix allocated to another country."
