Regarding the item on the $20 bill marked with a with a pro-Trump message, it is undoubtedly real, as multiple sellers on eBay list the rubber stamps used to create similar notes. The ones pictured in The E-Sylum appear to be home grown variations with the text handwritten. The rubber stamps have a similar message with an arrow that is positioned when stamping so that it points to the image of the White House.

On the other side of the political spectrum, someone is selling a "speech bubble" rubber stamp that says "Impeach Trump" that is meant to be stamped in such as way as to appear that the words are being spoken by George Washington (for the $1 bill) or whichever figure is on the note being used.

A while back I had a man buy something and he paid with several $20 bills. They looked just fine and I didn't turn them over, just put them in the cash drawer. Shortly after that we got to talking and he paid for another purchase with a $20 bill, but showed me the reverse with the stamp "Donald Trump Lives Here" on it. He proudly said that he had the stamp and was the person locally here in Colorado Springs who did the stamping.

Since I save notes with political or other stamps or writing on them, I saved the note. I then went to the cash drawer, and sure enough he had given me five with the stamp on them. Doesn't make much difference, they just go to the bank with our deposits I do prefer to collect notes of the $1, $2, or $5 denomination because they are cheaper to collect.

Incidentally, I'm still looking for one with Save the Spotted Owl stamped on it for my collection.

In the Sri Lanka Sunday Times I recently wrote an article on this topic since the Central Bank of Sri Lanka has had a strong campaign to demonetize them. A better Illustrated and linked version is posted on my web site.