Depends on how they were made (laying wheels versus backing in a trailer), the temp of the surface, and other variables. I have removed them both eaily with a sod hydo/butyl combo, and have also had them not come off no matter what I threw at them.
Concrete is sprayed with a cure. often they actually get sealed in if the people laying the concrete dont spray the cure the same day. often a fork lift driver runs accross and turns on it before the cure has been applied. Only breaking this seal will remove the marks.
this is the problem when you think they are in the concrete. cure is transparent.