Pick a source and go with what they use. Merriam-webster.com is a good one, but any will do. (They don't have a listing for L.A.)
My preference did not match my publisher's. They wanted LA, for instance, when to me that's the two-letter abbreviation for the state of Louisiana, and L.A. is the city in California. We also disagreed often on which compounds are two words, which are hyphenated, and which are joined.
Ultimately what you want to do is pick a style and use it consistently. The trend with most of the books I read seems to be toward omitting the periods in common abbreviations like the ones you use as your examples. You probably want to use all caps and a lower-case s for plurals, too: I checked the SUVs in the LA parking lot and announced the results over the PA system.
Maryn, whose edits were daunting