Many U-boats had insignia (bootswappen) painted on their conning towers. These insignia are often referred to as emblems. It appears that the first insignia was a metal Iron Cross mounted on the conning tower of U 9 during the pre-war period. This was applied to carry on the tradition of the famous U 9 of the First World War. As this was a plaque, it remained visible when it was over-painted at the start of the war. The first insignia to be painted on a U-boat conning tower was applied to U 30 on the 10th September 1939. It was a painting of a fox terrier called Schnurzl, who had often been on board during pre-war times.

Despite orders from the High Command for these insignia to be removed, no real effort was made to end this practice. As they had a morale-boosting effect for the crews, they became universally tolerated by the High Command. The insignia differentiated a boat from others in the U-boat fleet, so allowing the crews to have identification with their U-boats. Many crews even had metal insignias made, which they attached to their caps or uniform jackets. The use of these insignias was so widespread that boats without one were considered odd.

The insignias were inspired by a variety of sources. These included –

- Personal references to the commander. Examples include the “Snorting Bull”, which depicted the character of U 47’s commander, Günther Prien, and the snowman insignia of U 201’s commander, Adalbert Schnee (schnee means “snow” in German).
- Civic heraldry. Many German towns and cities sponsored U-boats, contributing money towards their construction. This scheme was called patenschaft. These boats often had the town’s crest painted, or mounted on a plaque, on the tower. U 201 had the crest of Remscheid on its tower, which indicated that it was sponsored by that city. Most of the boats in the series of twelve boats following U 201 were sponsored by cities. Often other personal insignia were applied in addition to these crests.
- Class symbols. A commander who had graduated from the Kriegsmarine’s Naval Academy would often choose insignia representing the graduating class. The Olympic Rings on U 20 and U 23 indicated that the commander of the boat had graduated in 1936. This was in reference to the Olympic Games held in Germany in 1936.
- Drawings mocking the enemy. U 34 had an elephant stomping on Churchill’s head and U 94 had a little animal taming a British bulldog.
- Patriotic imagery. Only in rare cases would swastikas be used as part of the insignia (U 123 and U 132).
- Good luck signs. U 99 actually had horseshoes welded onto both sides of the tower. U 48 had the opposite of having a good luck insignia – a black cat with “X3”, meaning “three times” - below.
- German folklore.