I recently started playing a cleric of knowledge and Suggestion has become their "signature spell." It helps that Knowledge Clerics kind of get it as a Channel Divinity at level 6. Fail a wisdom save? You've been Inceptioned.

I love the idea of each character having their own Signature Spell that they cast at every problem. For many wizards, this spell is Fireball, but even then, having a Fireball Guy in a party is its own fun.

I know Wizards get a feature called Signature Spell but no level 20 wizard has ever wanted just one more third level spell slot. I'll make a second post about this probably.