I wasn’t sure what he meant by “Hashmarks” either when I heard him mention this.
I would have to go back and listen, but at one point he was talking about placing bets for future hands out on the table (Which is clearly illegal). He said he would place his current bet say in seat 2, then at the same time place a bet on seat 3 and seat 4, but he said that the dealer knew that seat 3 and seat 4 bets were for the following 2 rounds, and not the current round. Then he said they put a stop to it. What casino would allow this in the first place I have no idea.
Anyway, if he was talking about the “hash marks” during this time, he may have been referring to the parallel marks that separate each seats betting spots.
I highlighted them in the picture below:
