I ended up with these out of a coin collection. What the heck would you call them? I think they were inserted into the larger bundles from the fed... bundle markers???
Brick labels. In the old days, forty straps of notes would be placed between two wooden blocks, with a label like this on one end, held together with steel bands. The whole thing was then wrapped in brown paper, with a second copy of the label on the outside. These were sometimes collected in the form of "label sets": the first and last notes of the brick were saved along with the brick label. You might want to check that collection and see if the relevant notes are included.... Sometime around 1990 (plus or minus a few years) the BEP switched to shrink-wrap for the bricks. They also added a level of packaging: they now wrap ten straps to a bundle and four bundles to a brick, instead of just forty straps into a brick directly. The Fed tends to break the bricks down into bundles before shipping them out, so you don't often see labels for anything larger than a 1000-note unit reaching the public any more. Here are two styles of the old paper brick labels, and a modern bundle label:
