Usually because our weekly matches are reasonably friendly all of the teams have gotten into the habit of telling the opponent to just call it if they'd like. Personally I'll use whatever is available if forced to actually use a marker. Although it's permissible, I try not to use chalk. I've used a beer, a shoe, a hot dog bun the other teams marker, crumpled up paper. I've reached in the trash can for an empty bottle or an old olive or broken glass. I might us a condiment left on the table, a piece of fruit. One time I took the smallest girl at the bar and had her lean against the table with hands next to the pocket on top of the table (as stated in the rules). My favorite though is from a pool hall we played at some years ago. We got the last order of wings to come out of that place, I took an old bone and boiled it, polished, engraved it, and sprayed it with clear coat. That thing is about 10 years old and I still carry it around. It gets used (as a marker) on occasion