No. It signals that you want a cup of coffee, you see they are offering coffee, and you are investigating whether or not that trade is something you want to engage in.

While you’re in the shop, you can observe cleanliness, ambiance, look at the menu to see if your favorite blend is available, see the prices and check your wallet to see if you can afford it, and so forth and so on.

You haven’t 'agreed' to jack shit until you step up to the counter, SPEAK to the barista, place your order, and pay for it.

Likewise, the barista (on behalf of the establishment) has the right to refuse you service if your credit/debit card is no good, if they can’t provide your request, if you’re behaving inappropriately, or if you’re breaking local hygiene ordinances (no shirt/no shoes).

The can also call the authorities to haul you away if you refuse to leave when asked.