O5 Resistance Symbol

Look to the right of the main entrance. See that blackened stone behind glass? The letters O5 carved there represent one of the cleverest acts of defiance in occupied Austria.

In 1938, Hitler annexed Austria. The country ceased to exist. Its name was banned. Anyone caught saying Österreich risked arrest.

But in 1944, a medical student named Jörg Unterreiner created a code. The O stood for the first letter of Österreich. The 5? That was the fifth letter of the alphabet: E. Together, O5 spelled out the forbidden word without spelling it at all.

Unterreiner and his resistance group began scrawling O5 on walls across Vienna. Hurried. Dangerous. Each mark a silent shout: Austria still exists.

This one appeared during the Battle of Vienna in 1945. In 1965, it was formally cut into the stone. The glass case came in 2000, along with a memorial plaque in the ground below honoring murdered resistance fighters.

What started as graffiti is now protected as sacred history. A reminder that two letters and a number can hold an entire nation.