what would the markings be on an Abrams in the Bosnia conflict?

It depends what division you want it to be from. It would have standard division and unit markings. The only additional markings would be IFOR (Implementation FORce), SFOR (Security FORce), or KFOR (Kosovo FORce), again, depending on when it was there. They would be in large, white block letters on the skirts of the tank.

Here is one in IFOR markings from 1-4 CAV, 1st Armored Division in DEC '95, crossing the Sava river.

Thanks Heavy, SFOR it is!