Window signs present a special problem, especially at liquor stores. This is due to lax regulation, loopholes, and uncertainty among inspectors. We all know how badly most liquor stores appear, as if they intentionally make the place look crappy to attract a particular class (low) of customer.
While the Regulations cover (and limit) wall-mounted signs, they exempt signs on the interior of windows. There is also a notion that signs made of "soft" material are also exempt, but I cannot find any specific exemption. Thus, while a sign made of Coroplast attached to the outside wall is covered (and prohibited), the exact same sign made of paper, cardboard, or vinyl might not be prohibited. But we've found that, even Coroplast signs stuck on the outside of windows might be passed over by inspectors, if they don't feel like taking action - like this mess in Pikesville pictured below.