When a student turns in a paper with no name, you can ususally just shuffle that paper to the end of the stack and then grade everyone else's paper first and input their grades first and thus the no-name paper will belong to the only blank spot on your grade sheet.

But if you get two no-name papers then you end up having to do investigative work that takes up your valuable time that you could have invested doing something more fun and enjoyable.

There are a couple ways to minimize this sort of thing that you might want to try:

1.  Include a statement in your syllabus that if a student turns in a paper or test with no name you have the right to dock them 5% on that paper.  While you really don't want to do this, (it creates bad will), the mere fact that you include the statement in your syllabus will help make sure that students put their name on their papers.

2.  Just before the last question on a test, include the sentence "Did you put your name on this test?"  By sandwiching the question between two questions you get their attention.  Or for a more clever approach you can include the sentence, "Did you put your name on this test?" as one of the wrong answers in a multiple choice test.

3.  In the written instructions for the exam, include "Put your name on this test" as the last instruction prior to beginning the test.

4.  If you are giving a signed test, and the students are writing what you sign, then write your basic instructions on the board (or include in your overhead projection) "Put your name on your paper" at the top of the list, and then again at the bottom of the list.  Example:

Quiz Instructions:
Put your name on your paper.
Put today's date.
Put the quiz number: ____
Number 1 to 20.
Did you put your name???