You probably found the weird pictos in during the expedition festival by spending a token with Tom—it's a very unusual quest item that offers no clue what to do with it. However, considering you get them right before you set off for the continent, it's clear that you won't be using them in the city of Lumiere.
That leaves you with a bit of a quandary; you've got the whole rest of the game to explore but no clear indication of what this item is used for. If you want to skip the finding out phase, here's where to use the weird pictos in Clair Obscur: Expedition 33 and what they'll get you.
How to use weird pictos in Clair Obscur: Expedition 33
You won't be able to use the weird pictos in Expedition 33 until you reach the Gestral Village, even though you found them before even setting out. It's not that far away, but getting there will require a reasonable amount of story progression, successfully navigating the first few areas and beating multiple bosses.
Once you arrive in the Gestral Village—don't worry, the story will literally guide you to this [[link]] location—you'll want to head into the bazaar on your left and look for the Gestral Merchant behind the counter talking to a customer just by where you enter. This is Jujubree and he'll [[link]] let you browse his wares once you speak to him.
After you close the shop menu, he'll notice your weird pictos and ask to take a look at fixing them. For me, this added three levels to my Augmented Aim picto, taking it from level two to level five. I tried unequipping all my pictos to see if that made a difference, but it didn't. You might not have acquired Augmented Aim, so there's a chance that this upgrade might be applied to another picto in your collection.
Either way, three levels is a big bump. I'm not sure if there are other weird pictos you can find in the game, but if you do, bring them back to Jujubree for even more free levels.