Let me just begin by saying this: I love dive bars. I would much rather go to a dive bar than some packed club or trendy (a.k.a.
expensive) bar. I like the kind of place where I can wear jeans, Batman t-shirt, and a ponytail and still be one of the best-dressed people there.
Sometimes, when first visiting a bar, it can be hard to tell if you are for sure in a "dive bar" or not. Of course, there are your dive bars that are recognizable from a couple of blocks down the street. But there are also some that are borderline dive bars. If you visit these bars during off-peak hours, it may be hard to distinguish if it is indeed a dive bar.
I have found that the best way to clearly tag a dive bar is by examining the restroom. I have an advantage because women's restrooms either "ARE" or "ARE NOT" dive bar bathrooms. There is no in-between.
So... Here are some photos to help you indicate whether or not you are in a dive bar by only checking out the women's restroom.
Number One: No soap dispenser; just a bar of soap resting on a papertowel on the side of the cigarette-stained sink. (Although the fact that there is soap at all means that you are in a higher-class dive bar.)

Number Two: Toilet seat that is not attached to the toilet itself. (Lucky that in a dive bar, women usually "hover" anyway.)

Number Three: Religious message scrawled on the wall, complete with witty retort quipped beneath.

I hope this helps you to identify the next dive bar you visit. Be sure to have a PBR (preferably in a can) for me!