I think Hezekiah's Signet Ring and Jerusalem Tower were both classified as restricts. I'm not sure how I feel about that, as my understanding of Restrict was that it essentially stopped players from certain game actions. Searching is a game action to be sure, but I think that restricts should only stop those game actions that can be done without special abilities. Since there is no way to search without using a special ability (as opposed to game actions like drawing or making rescue attempts, which are often done not as a result of a special ability) my preference would be that HSR would either be ruled as a prevent (Play As: Prevent search abilities used by opponents) or a protect (Play As: Protect all decks and discard piles from search by opponents). My vote would be for prevent. However, like I said, I believe the current rule is that it was made a restrict, and the Play As should read: Restrict opponents from searching any deck or discard pile.
Altar of Dagon is unquestionably a Protect. It has been a rule for years that cards that say "No X can be Y'd" are essentially ruled "Protect X's from Y". I don't recall that ever having changed.
Covenant of Abraham should be ruled a protect as well. The Play As there is incorrect based on the wording similarity to Altar of Dagon, Blue Tassels, etc.