I'm involved with a project that needs a few icons to represent some categories. Some of them aren't that difficult to represent graphically, however I'm having a hard time thinking of how time is represented graphically.
Specifically, I need two simple icons to represent both past and future. I tried looking up other representations, but the best I can find are arrows pointing left and right. However, these are very unclear and would just be confusing to the user.
My question is, how has time been graphically represented throughout history?
EDIT: This edit is for my specific purpose. However, I'm still really interested in the bigger question of 'How was time been graphically represented'.
Since I didn't provide context, I'll clarify a bit. I'm working on an app that allows users to take a picture of something, tag it with 1 of 5 categories, and then upload it so that everybody can see all of these notes (optionally sorted by these tags) on a map.
The purpose of the app (right now) is specific to Madison, Wisconsin - and is trying to showcase the cool things the city has to offer.
The 5 tags are Madison Culture, Must Do Things, Innovations at UW, 'Stories of the Past', and '100 Years From Now'.
Stories of the Past are cool things that have happened in the city, excluding inventions and such (innovations) - so not really 'stories' in the book sense.
Past: I've thought of making a moldy tome, or silent film representation of our famous State Street. Future: A flying car by the state capitol.
The problem with these ideas, is that they are only supposed to be small annotations on the map, and I'm afraid that these are too detailed and will be impossible to decipher.