"?" is "IMI"
"+" is "AR"
That's punctuation . . .
prosigns really have their own idiomatic meaning, rather than being punctuation or abbreviation.
I think it comes from "procedural signals".
The two letter without a space is just a shorthand way of describing them . . .
. . . tho ironically for idioms, quite a few of the non letters seem to come directly from American morse.
I'm not so sure how many are part of lcwo's repertoire, but if you learn the letters then prosigns shouldn't cause you too much trouble . . .