When you end a sentence with "a.m." do you put two periods after the a.m. If it were a different punctuation mark I would (see previous), but it looks silly to write a.m..

Thanks!

According to the Gregg Reference Manual #512,

"If the abbreviation ends with a period, that period also serves to mark the end of the sentence. If the abbreviation ends without a period, insert one to mark the end of the sentence. NOTE: Ordinarily, placing an abbreviation at the end of a sentence that makes a statement poses no problem. However, when the correct form of an abbreviation is the issue under discussion, place the abbreviation elsewhere in the statement. In that way the reader will not have to guess whether the period that marks the end of the statement also marks the end of the abbreviation."

So, yes. The period that ends a.m. serves as the ending punctuation. If you want to avoid confusion, simply place the a.m. somewhere else in the sentence.