Leuchtturm Dornbusch on the island of Hiddensee in DDR days

Yes, those are DDR border guards patrolling to prevent citizens from escaping the freedom of the workers' paradise to the slavery of the capitalist west. The 28-metre tall lighthouse, now painted white with a red top, was put in operation in 1888; the beam shines for 45 km over the Ostsee (Baltic). It can be visited. More info