Protesting is About Attention! Use that to your advantage. Protesters love the press. It can be a relatively simple proposition to get a press pass that will get you through/past protests that completely block traffic. Afterwards, ask them for a letter stating you have written for them, etc.
Write an “About” page or article telling people that this blog is for covering local protests or demonstrations
Design your own press ID using a template (Here’s an example template). Don’t lie on the pass. It’s not necessary.
Print it on a solid plastic card. There are tons of companies that will do this for a few bucks. (Here are a few) I had mine printed locally for about $.80 each.
Throw the ID on a lanyard or in an ID armband and stash it in the glove compartment for whenever you may need it.
If you have to use it, present it with authority! It has never failed me, even under the scrutiny of armed soldiers at roadblocks.