My husband insists that you can combine the +1 to all skills bonus from Markings of Isis with bonuses from other cards. He says it's "like putting improvement tokens on the card." I disagree. We need a ruling! TIA

"+X" effects typically do not stack (whereas "+X" and "add additional dice" effects do), so I would say that you're correct, they do not combine/stack.

He may use one effect that provides a bonus. If multiple effects provide a bonus, he uses only the highest bonus.

7 hours ago, KBlumhardt said:

"+X" effects typically do not stack

Not only "typically", they never stack. There are no exceptions.
And there will be no exceptions in the future. Why? Because the "roll X additional dice" notation is there and it only differs from "gain +X" in this one aspect - "additional dice" stack.
The sole purpose of having these two very distinct notations is to easily distinguish bonuses that don't stack from those that do stack.

@Raj1984 Markings of Isis could say "Gain +1 [Lore], +1[Influence], +1[Observation], +1[Strength] and +1[Will]" and it would be an identical effect to the current one. "All skills" is just a more sensible notation when you're referring to all skills.

It doesn't stack with any other + boosts. Just your base and any improvement tokens. It's a handy little beast because it works on any skill, but it still doesn't stack.

He's probably confused because, as a Glamour, it's "always active"