prijavljivati

1. (prijavljivati se na + acc.) to sign up; to register; to apply; to register someone
   Svake godine se prijavljuje na maraton. — He signs up for the marathon every year.
   Kandidati se prijavljuju do kraja meseca. — Candidates apply until the end of the month.
2. (+ acc., to authorities) to report
   Komšije stalno prijavljuju buku policiji. — The neighbours keep reporting the noise to the police.
3. (prijavljivati se, in a system) to log in
   Ne prijavljujem se na taj sajt preko Fejsbuka. — I don't log in to that site with Facebook.
4. (at a hotel, airport) to check in
   Putnici se prijavljuju na šalteru broj pet. — Passengers check in at desk number five.
5. (officially, + acc.) to declare; to register
   Stranci prijavljuju boravište u policiji. — Foreigners register their address with the police.
   Da li nešto prijavljujete na carini? — Do you have anything to declare at customs?

In the senses “sign up”, “log in” and “check in” the verb is usually used with se.