I don't use a push-pin call, but for my box calls I have used a half moon of red chalk. The old timer who got me into turkey hunting back in 1988 told me to go to a hardware store or lumberyard and get red or blue chalk. I picked one up for a dime back then!!! I keep it in a latex surgical glove (ziplock bag will do, too) in my vest. Stuff has no oils and last forever.
I think I still have some of that original half moon around somewhere.