Ruse is a city in northern Bulgaria, located along the Danube across from Romania. On the east side, there's a bridge which forms the border point with Romania, the Ruse-Giurgiu border crossing.
Hitching out
North towards Bucharest (Romania) E 85
Reach the Ruse-Giurgiu border crossing by foot or via a local bus and get a car at least over the bridge.
South towards Veliko Tarnovo
If you are hitchhiking with a sign, write "В. Търново", as that is what the Bulgarians and their road signs shorten the name of Veliko Tarnovo to.