The arms show the lion of the Counts of Berg, who ruled the area for many centuries. The oak tree refers to the (former) forests in the area. The base shows symbols for industry, a wheel and miner's tools, but also 2 swords for the metal (knife) factories.
www.zeitspurensuche.de and 
This image is taken from www.ngw.nl – Heraldry of the World –  an international civic heraldry site by Ralf Hartemink.
Stadt Dorp



This  is a retouched picture, which means that it has been digitally altered from its original version. Modifications: Vectorized.  Modifications made by Juergenk59. The original can be found here: [1].