What does an auxiliary plate beneath a STOP sign displaying the text '50 m' (e.g. STOP + 50 m) indicate?

1. In 50 metres, you will reach an intersection governed by an octagonal STOP sign (Najava znaka STOP na 50 m)
2. You must stop immediately where the sign is posted and wait 50 minutes
3. The stop sign is valid for 50 metres past the intersection
4. Speed is limited to 50 km/h for the next 50 metres