What do you mean by explicit and implicit signals?

An explicit signal is stated directly while an implicit signal is implied by inference. Barricades and "Bridge Out" signs set up to prevent access to a washed away bridge would be an explicit signal. Seeing fast moving water covering the floor of the bridge would suggest that drag racing across it might wait.

Explicit is something that is expressed, said aloud in so actual words. Implicit is not expressed but implied.