@Elderberry @libertybele @mystery-ak In Texas and likely every state, one cannot just walk in a polling place and say he/she is a poll watcher.
Each Democrat and Republican Chairman in a county may appoint poll watchers, one poll watcher for each Precinct Polling place, or not use them, or use them at specific Precinct Polling places. It is up to the Chairman whether to use poll watchers or not. If using poll watchers, the Chairman must instruct the poll watchers what they can and cannot do at a polling place. I know what those poll watchers can and cannot do, but won't post them here unless someone wants to know what they are.
Also, the poll watcher has a document from the Chairman saying this person is a poll watcher. The poll watcher must show this document to the Judge of the polling place.
There are laws and rules that must be followed in an election and that is true for Poll Watchers, too.
A poll watcher at a mail-in ballot drop off location goes through the same process as above. In this case, their documentation to be a poll watcher would be shown to the early voting clerk at that location.