The gold standard of two-color ramp. Signets are arguably the best mana rocks in Commander after Sol Ring and Arcane Signet, and Azorius Signet is no exception. The reason they shine is mana filtering: you spend a generic mana and get back two colored mana, so you net +1 mana while also fixing your colors. That filtering is underrated — it turns excess lands into precisely the WU you need for double-pipped spells.
Who wants it: essentially every Azorius (or Esper/Bant/Jeskai/multicolor) deck. Control, blink, stax, flicker, spellslinger — if you're playing blue-white, you want consistent T2-T3 acceleration and color smoothing. It ramps you into your commander and counterspell mana ahead of schedule.
When to skip it: mono-color decks (Arcane Signet or Mind Stone is strictly better there) and ultra-aggressive low-curve decks that don't need ramp. It's also slightly weaker in heavy-removal metas since rocks get blown up — but the upside almost always outweighs that risk.