The sign you mentioned, Base plate 750 x 500, is a reference to a specific type of sign that provides additional information regarding road rules, restrictions, or guidance related to traffic situations. However, without the image, I can't provide a specific analysis of the sign's meaning.

In general, base plates can indicate various things depending on the accompanying symbols or text. They might show information about speed limits, parking regulations, or special lane uses, among others.

If you have a specific traffic sign in mind or an image you'd like me to analyze, please share, and I'll provide a detailed explanation of its meaning according to German traffic laws!