How can you tell if its "safe" to escalate with a woman? What signs do you look for?

So, i know when picking up women, they aren't gonna flat out say "You can touch me, you can kiss me, etc.", but it's a major mood killer to ask for permission.

What signs do you look for?

If you approach someone in a bar, how can you tell if its safe to escalate? What signs do you look for?

This is something that's kinda new to me, so...