An Etymological Dictionary of the German Language/Annotated/Schild
Schild (1.), masculine, ‘shield, coat of arms,’ from the equivalent Middle High German schilt, Old High German scilt, masculine; a common Teutonic term; compare Gothic skildus, masculine, Old Icelandic skjǫldr, Anglo-Saxon scyld, English shield, Dutch schild, Old Saxon scild. The word first signified ‘signboard’ in early Modern High German. The specifically Teutonic term skildu-s (from skeldhus, skeltús?) cannot be traced farther back; it can scarcely be related to schallen (Schild, literally ‘that which gives a loud sound or resounds’?).
Schild (2.), neuter, ‘signboard,’ Modern High German only, a variant of the foregoing; hence Schilder- (neuter stem) in compounds such as Schilderhaus, ‘sentry-box.’