I use this as a tag: ##
I use this tag as that character is easy to quickly type on my mobile device, and easy to find on the desktop to tag after.
I have found what seems to be a bug, in that I cannot search for this character using the most recently updated version of evernote, or evernote legacy.
I can have all notes tagged with ## listed, but I cannot simply search for ##
I have also found that I cannot search for other characters such as $, %, *, etc