[MacGuffin]

Hickeys usually have certain signs you can look for right away to tell if its going to mark right away. If it is just a red area, kind of like a light sunburn might look, then it is fine and will go away within in a couple hours roughly, depending. If it is a really dark red or purple-ish hue (as in there is lots of blood flow to that spot, not bruising necessarily), if there is darker spotting within the red area, a darker area within the light red part, or just plain up bruising (it can happen), you will probably have a hickey. Regardless, wear your hair down for a few hours before checking again, just in case.