With the Latis distribution, I'd like to take a moment to mention that Luster Purge and Mist Ball (70 BP, 5 PP. 100% Acc, 50% 1-stage effect, 0% usage) could have been upgraded to be more like Seed Flare (120 BP, 5 PP, 85% Acc, 40% 2-stage effect, 100% usage)
Would personally rather see them become 90 Power to they're on par with Psychic. I personally think that a Signature Move should either be equal to or better than the usual move that Pokemon would have if it didn't have the Signature Move. Looking through some other Signature Moves:
Meowth family: Pay Day (40 Power Normal-type move that secondary effect is giving you money equal to five times the user's level. Bleh, there's usually quicker ways to make money not to mention you're given enough money during the game you don't need to money grind either. Sadly Pay Day is competing with Return or at least Slash so it would need a major overhaul to be considered over them. It's also entirely useless on the Alolan Meowth family)
Kadabra/Alakazam: Kinesis (Decreases target's Accuracy by 1 stage... and has an Accuracy of 80. Like, why? You would think a Signature move for Alakazam would be pretty powerful, but it's just a glorified Flash!)
Exeggcute Family: Barrage (A multi-strike Signature Move could potentially have been useful... if it had more Power, got STAB, and was the right offense category. Like make is a Special Psychic-type Tail Slap and it could be decent... if they also got the Skill Link Ability...)
Alolan Exeggutor: Dragon Hammer (At best Barrage had the excuse it was a Gen I move where GF had no idea what they were doing... Dragon Hammer doesn't. Like, at least make Alolan Exeggutor a Physical attacker instead! Why should it use Dragon Hammer instead of Draco Meteor/Dragon Pulse?)
Octillery: Octazooka (With there being Surf and Hydro Pump, Octazooka ought to up its Power from 65. Not helping it a lower Accuracy, the secondary effect is nice though doesn't really justify the Power and Accuracy loss)
Delibird: Present (Why? Just why? Only way of saving this move is a complete overhaul of what it does)
Hitmonlee/Hitmontop: Triple Kick & Rolling Kick (Triple Kick is a multi-hit move which max Power is 60 if all strikes hit. A Brick Break is more powerful and has a useful secondary effect on top of that. Not to mention they learn Close Combat (And Hitmonlee gets Jump Kick & High Jump Kick). Rolling Kick has the workings of a good move, the 30% chance to Flinch is nice but has 60 Power and 85 Accuracy. Need to either pump up the Power or Accuracy (or both, Air Slash seems to have no problem being 75 Power and 95% accurate)).
Makuhita family: Smelling Salts (Nothing wrong with the move itself, just that it doesn't get STAB. Plus they don't have a good way of Paralyzing the opponent, best they have is Force Palm with only a 30% chance (and gets STAB)... but why do all this work when they get Close Combat, Brick Break, and even Wake-Up Slap which all get STAB and good power?)
Latios & Latias: Mist Ball & Luster Purge (It's just that low Power which is a problem, make it 90 like Psychic!)
Heatmor: Fire Lash (While Heatmor's Attack is only 10 points lower than Special Attack, still why aren't we using it's strongest offense stat?)
Helioptile family: Electrify (Would have really been interesting if the Helioptile got the Electric-type absorbing Abilities)