How do you mark your balls?

(This conversation took place in August while on vacation.)

Dad: I mark my balls with a ...
Hubby: I mark my balls with a ...
Dad: Hey, I wonder how BIL marks his balls...
Me: Wha? (I walk in in the middle of this conversation and burst into giggles.)
Hubby: What is so funny?
Me: What balls are you marking?
Hubby & Dad: Golf balls! (Realizing how this all sounds, they start laughing hysterically.)
Me: Imagine this conversation not understanding it was about golf! I would mark mine with shamrocks.

We discuss that we think BIL might put like a happy face or something on his balls. However, this could be too much work. It goes on and on.

So, golfers, how do you mark yours balls?