The legends are CONSTANTINVS P F AVG and SOLI INVI-C-TO COMITI. Constantine is laureate and cuirassed, not draped (I don't think!). There are no letters or symbols in the fields. This means it is Ticinum, and the mintmark is TT.
Unbelievably, there are 5 possible attributions in RIC. I don't know what the authors are thinking with the 'standing left, facing right' thing. Ignoring the examples on Ocre, as RIC seem to have confused even museums: Sol doesn't have a whip, so it isn't RIC VI Ticinum 135a. Sol is standing right, so it isn't RIC VI Ticinum 128, RIC VII Ticinum 3 or RIC VI Ticinum 133. Sol is standing right with his head left and the chlamys draped over his left shoulder, which is RIC VI Ticinum 131a http://numismatics.org/ocre/id/ric.6.tic.131a
That's my guess, anyway!
Unbelievably, there are 5 possible attributions in RIC. I don't know what the authors are thinking with the 'standing left, facing right' thing. Ignoring the examples on Ocre, as RIC seem to have confused even museums: Sol doesn't have a whip, so it isn't RIC VI Ticinum 135a. Sol is standing right, so it isn't RIC VI Ticinum 128, RIC VII Ticinum 3 or RIC VI Ticinum 133. Sol is standing right with his head left and the chlamys draped over his left shoulder, which is RIC VI Ticinum 131a http://numismatics.org/ocre/id/ric.6.tic.131a
That's my guess, anyway!