I believe it was a vinyl embossing machine for making signs. The red part sticking out was some remaining partially embossed plastic, so it had definitely been recently used.

I was very tempted to take it, but I had no idea how many letters were left in the definitely partial set, and it was going to be very heavy. And I would have been picking them up for ages all down the street, someone had really thrown them around.

I hope someone found it and gave it back its purpose though.