Agreed - just as some use capitalisation to make distinctions. One way to ensure no searches/hints are likely to throw up whole groups of irrelevant names is to use a short, simple indicator, eg Fnu (for first name unknown) and SNU (for surname unknown). This has the advantage of being easily printed.
Whatever you use, though, it's a good idea to check what a search is actually looking for (Edit Search), and amend the first or last name boxes if it is looking for something strange!
PS: sorry - I overlooked sturdy2's post, above!