Girls what are the sure fire signs a guy should look for to determine if you are immediately down for sex?

I am not talking about the general signs of liking or interest
I actually view the general interest and immediately down for: sex are two different things.
Advice out there normally focus on the general signs of interest so I actually want to hear some advice from you girls like what are the signs a guy should look from a girl to be sure that this girl is down for sex immediately? How do you signal to a guy for that?
Girls what are the sure fire signs a guy should look for to determine if you are immediately down for sex?
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