Didn't notice that until you asked, but my Cedar Point, OH has what is usually used on pieces that don't have flags, but are hand-numbered on a sticker on the bottom of the piece. Event pieces usually have that kind of sticker. The one on my Cedar Point does not have the underscore and appears as # /2500. Maybe HL is using one style on all pieces they produce to save money on printing.

I can't say if the Windmill Point, VT has one of these as well, as it's not readily accessible from the curio cabinet where it's displayed.

Sandy