Whats this behind the seat?

[Hawssie]

I just bought a 1970 c10 from a school district. Can you believe in CA. they were still using these trucks until recently. They had 4 one long bed 69, and 3 short beds 69,70,71. I bought the 70 for $1860. I wanted the 71 but it was a short bed ordered without a bed and had a utility bed on it. Needs a lot of body work esp. on the bed sides. At least no real rust and almost all original even the owners manual. Anyways I took out the bench seat to clean it and make sure found no rust.(there was just a bit on the d.s. kick panel. Was getting ready to put back the seat and i found this old piece of paper woven into the seat springs. It looks like it came from the assembly line or something. Maybe because the truck was sold right around the corner from the Fremont CA, plant?