I can be on firmer ground with this one, since I have a semi-proper reference for it - it's in Sear Vol III. It's a billon antoninianus, reverse: VIRTVS PROBI AVG (the Valour of Emperor Probus), emperor on horseback pacing left, bound captive beneath horse's front hoof. KAA in exergue. Listed in new Sear as #12075, attributed to Serdica mint, 277 AD. Sear gives the references as RIC 886, Cohen 928.
A simiar one from WIldwinds.
"KAA" isn't a mintmark, in the sense of being an abbreviation of the mint city. "KA" is basically the denomination/fineness mark, meaning "20:1" or .050 fine silver. The second "A" is the officina mark (in this case, first officina).
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis