Most customers are okay with "close" on font matching work. But some tasks require things to be right on the money, such as replacing something like a damaged channel letter face. A typeface of a given name may have variants that are not identical to each other. For instance there's two different variants of Papyrus out there, the original one made by Letraset (the good one) and the ugly version often bundled in with MS Office (it has much smaller lowercase characters). Helvetica has multiple variants and not all of its "clones" (such as Bitstream's Swiss 721 or URW's Nimbus Sans) are identical.
	
		
			
				Andy D said:
			
		
	
	
		
		
			What about when the customer takes a picture of a 
sign you did for them and uses that? I don't see any reason to make it easy
on another shop to copy your work.
		
 
If a customer takes a picture of a finished 
sign we already built for them and shows that image to a different 
sign company they really haven't done anything wrong. The situation is not an all cut-and-dry thing however. But normally if we create a design with a new logo we did in-house and the customer buys a substantial 
sign based on it, then builds his branding around it we normally sell them the rights to that logo as part of the 
sign deal.
Now if they decide they're going to open another location and have someone else make the 
signs, it's okay for them to provide logo files we gave/sold to them. But we don't have to provide the rival 
sign company with any of our original production files, specs, etc. We still retain a copyright on that stuff even if we sold a logo in the drawings.