označavati

1. to mark; to label
   Nastavnik crvenom olovkom označava greške. — The teacher marks the mistakes in red pen.
   Na mapi označavamo mesta koja smo posetili. — We mark the places we've visited on the map.
2. (of a word or sign) to denote; to mean
   Šta označava ovaj simbol na etiketi? — What does this symbol on the label mean?
   Crveno svetlo označava opasnost. — A red light signals danger.
3. (of an event) to mark; to signal
   Ova odluka označava kraj jedne ere. — This decision marks the end of an era.

The perfective is označiti.