Weird plaque? [ENDED]

Was it the power station from the early 1900s? I think this is a replica of a practice plate the riveters used to practice before they actually went out to do the riveting on the construction site. You probably know riveting was a hard task that required a team of highly trained specialists, so the practice was to have a plate with different rivet shapes and practice to get the feel of getting a rivet into a proper hole. The round ones are the usual ones, so there are more of them to have more practice and the practice rivets and holes were actually made smaller, so that a riveter would feel doing an easier task when in the yard already.

The plate have been placed on the power station as a memorial for injured riveters or as a motto of careful preparations and consideration before undertaking a task.

In what part of the building it was? It doesn't make much sense to me :/ Maybe it has nothing to do with the building and was added by someone. Maybe it is part of one of those geocaching games.

The plaque is a simple makers mark for the five engineers that oversaw the construction of the power station. Not many people seem to know that professional engineers all have a unique set of marks made from stainless steel punches (similar to hallmarks in jewellery).

For those who want to check any set of shapes that one might find randomly a dead give away to recognising a makers mark is the simplistic beauty of the lines and the geometric precision involved. The history of using marks can be traced all the way back to ancient Chinese builders. (see the picture taken from a Han Dynasty tomb). There has been a stylistic change over the centuries but the tradition has been kept up.

View attached image.

It's secret directions for the real meeting place for a secret society of mathematicians/engineers. New members are at first just thought the secret code and pointed to the power station. To be considered worthy, they have to figure out, why there is no one at the specified meeting place.

Hey, I'm pretty sure I've seen this back in my kindergarten years..
Every teacher had a couple of these for each of their classroom and used to pull out pills from those holes and gave to the students: the more good they had been, the more sides the pill had.

Perhaps you found the remains of an old store/museum/other where they hung a copy as example.

New clues indicate that it corresponds with a countdown, something about less than 6 hours to something.