Shields with a message
Literally, to have something on your shield, "etwas im Schild führen" does not bode well. It means a person is up to something, is scheming. Foot soldiers would carry shields, often made of wood or animals hides, to fend against attacks. Friend or foe? Often, shields would display a coat of arms, or a motto — making the combatants' allegiance known to all.