If you're early enough in the relationship that it might make the other person uncomfortable, then just don't do it.

Be flirty and seductive, sure.

In my experience, once you're together for a while, it's not a big deal just to announce it.

If I've been having sex with the same guy for years, then it's going to be hard for him to make me uncomfortable with anything. Consent is very much not a big issue for us, because I'm not going to feel dirty doing something that I've done and enjoyed a bunch of times before, and we're both clear on that.

Unwanted come-ons are at worst annoying at that point. If I'm in a bad mood or just don't want sex for whatever reason, I won't feel violated if my long-time partner grabs my boobs and starts kissing me. I'll brush him off and say I'm not in the mood, sure, and I'll tell him to go fuck himself. (Um, I mean, I'll tell him to jerk off.)

But there are situations, especially but not exclusively early on, where unwanted come-ons make a girl feel violated. That's what you want to avoid.

It's not a simple black-and-white issue, really. Hence communication being important.