I could say when you see her at the ballpark swallowing hot dogs whole but then again...
In high school they used to say it was when a girl smiled and you saw pubic hair stuck in her teeth but that's not a guarantee that she hasn't been out with her girlfriend lapping the taco.
I reality, the true sign she loves sucking cock is when she undoes your pants after a few minutes of making out and starts giving you an unsolicited blowjob. That tells you she's a keeper.
In high school they used to say it was when a girl smiled and you saw pubic hair stuck in her teeth but that's not a guarantee that she hasn't been out with her girlfriend lapping the taco.
I reality, the true sign she loves sucking cock is when she undoes your pants after a few minutes of making out and starts giving you an unsolicited blowjob. That tells you she's a keeper.