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Deutsche Welle

Berlin police say the window on the outside of the memorial was broken, most likely with a stone, Associated Press reports.

The window allows visitors to look inside the concrete memorial at a video installation that shows a same-sex couple locked in a perpetual kiss.

The simple grey rectangular stone across the street from Germany's national memorial to Jewish victims of the Holocaust was inaugurated in May after years of controversy.  

More than 50,000 homosexuals are thought to have been convicted under the Nazis "because of their sexual orientation," with thousands of them sent to concentration camps and murdered.

Current research suggests 54,000 men and women were convicted of homosexual acts and about 7,000 killed in the camps.

Monument's window targeted

The monument, designed by Danish-Norwegian artists Michael Elmgreen and Ingar Dragset, contains a window that invites the visitor to look inside and see a film of a homosexual couple kissing. The film changes every two years. 

In August, vandals broke the window in a similar manner to the recent vandalism. That round of vandalism led to protests denouncing homophobia attended by more than 100 people, including Berlin's openly gay mayor, Klaus Wowereit.