No, it's not your imagination - yes, there is a cat in Assassin's Creed Mirage that has a very deliberate Assassin's Emblem on his snout.
Even more amazingly still, the cat isn't even a work of fiction created by the dev team. It turns out that a fan shared an image of the sweet kitty after he "recently crossed the rainbow bridge" and after bringing him to the attention of the team and offering "coffee and Timbits" to any dev prepared to immortalise the cat in the game, it seems Ubisoft did precisely that.
"Am I reaching at straws here or?" asked suckashelfboi101 on the game's subreddit, seeking assurances that they weren't just seeing things. "Is this cats face supposed to look like the Assassin Emblem or what because it’s all I can see. Maybe something the devs put in for fun?"