The metal plate, which appeared three days ago without the knowledge of the central or local government in Croatia, bears the inscription "Sarajevo University Clinical Centre, Main Branch for Recreation, Cavtat".
"Next Monday I will file a suit for trespassing because I am the only legal representative of the hospital. I will inform the Croatian Interior Ministry of the incident in writing," trustee Pero Vican said on Friday.
The ownership of the hospital is the subject of a legal action brought by the Republic of Bosnia-Herzegovina before the High Commercial Court in Zagreb.
The hospital is claimed by the Sarajevo University Clinical Centre, which argues that it was illegally stripped of its ownership by decision of a court in Split in 1993 in time of war when ownership rights should be held in abeyance.
Bosnia-Herzegovina wants the status of the hospital to be resolved as part of a bilateral agreement on property-related issues.
The Dubrovnik Commercial Court recently accepted a bid by the Cavtat-based firm Konel to buy a piece of the hospital grounds. The rest of the grounds will not be put on sale until completion of the legal proceedings.