Heavy is a supertype that restricts a player to play no more than one heavy card or spell per turn.

While I like Heavy as a concept, Wizards is not a fan of printing drawback-only abilities. Obviously we don't need to do everything exactly as Wizards would (they would never print Anydria and probably won't revisit the mechanic), but it's something to be aware of nonetheless. I also think this would need to cost in order to enter the battlefield untapped, even with the drawback.

Eh, they put it on all their lands already.

So they do.

But they don't say it on the card, so people don't realize what's going on.

Okay, so I realize that it's a drawback, but Azorius Signet was kinda good just being a ramp spell even if you couldn't chain it. While the supertype reduces abuse, it doesn't prevent these particular cards from being format warping.