This is above the power level Wizards currently finds to be acceptable.

Mm... it's true. There's a reason why Return to Ravnica didn't feature any two cost signets. Development articles from a couple years ago have mentioned that wizards thinks Dimir Signet is too good a card. Though we've spotted occasional exceptions to the rule (Everflowing Chalice for example), they've been keeping to colorless, and never more than one in standard.

The Ravnica-block signets were are already toeing the line. This is definitely over-the-top. At it might be okay, if it was uncommon.

Yeah, I too want the signets to return - but this is better than them - which is a step too far I guess.

If your set really needs mana wash, you could probably get away with this if it had an activation cost of . (Maybe could even be cheaper to cast then, as it's often not useful.)

For mana generation - I wonder if making this a creature too, and thus more vulnerable, would make it more acceptable?

signets were bad because they take up too many slots. this is fine as a 1 of

But... name a deck you wouldn't smack 4 of these into?

That also doesn't explain why wizards was willing to take up 5 slots with Obelisk of Bant's cycle and 10 slots with Orzhov Cluestone's cycle, but not print any common signets since 2006...

Wizards doesn't want cards with CMC ≤ 2 to ramp and color fix in colors other than green.
Personally, however, I like the current design.

Ha! OmegaParadox, you're making me look like my set is going to copy you. I have a cycle of dual lands that do exactly this (such as Frozen Delta) designed in 2009, that I'm putting up tonight. ;)

By the by, I'm going to be attacking my own design tonight, but that doesn't mean I don't like this card. It's a good idea... it just doesn't work on a cycle of rare lands.