I don't see any reason to think something extra was on the tread? I think the shoe pushed down on something and that faint pattern can be seen throughout the photo. It's not the texture of the tread, but of what the print was impressed on.
But many rubber treads are nonslip. I think that's the primary reason for making rubber soles.
I feel like I'm really missing what you are seeing. I'm so sorry!
I understand and agree. I think the cloth is what received the imprint -- maybe it was a victim's clothing, or other clothing or cloth at a crime or accident scene? (speculation, obviously)
I'm not even positive the pattern we are looking at came from footwear. I mean, that's how it was described to us and it well may be, but it could also be an assumption or a working theory. I'd love for the OP to clarify what exactly is known and what is assumption or speculation.
If not footwear, what else could it be? Presumably it was used to hit or press onto the background cloth.
I had the thought about playing cards as well.
I also see a rough likeness to the MLB baseball logo, so maybe a bat? Or a logo from a cap?
I disagree with a poster above that we are seeing the entire image of whatever made this. If it was made onto a narrow surface such as a person's arm or leg, the area of impact could be smaller than the entire print/logo/whatever, due to the curve of the limb, if that makes sense. Like if someone stepped on a person's arm crosswise, the impression left on the sleeve won't be a full footprint, because a foot is longer than an arm is wide.
My curiosity is killing me on this one and I hope we learn more and eventually figure out what made this imprint!
MOO