Factorio

I had a very short and consistent scheme for a while. No text, just icons.

{materiel icon}{chest icon}

For example, one station provides iron plates to the rail network (loads onto train), the other requests crude oil from the rail network (unloads from train):

Downsides: Some uncommon icons can be hard to read. Some liquids are similar in color and hard to identify when seen alone.

So later we changed to a better readable format. Examples:

[L] Iron Plates

[U] Crude Oil