Ah, I think I may have used in/out inversely to you when I set up trains.

"copper in" is where copper is put "into" the train system "copper out" is where copper is dropped

For production facilities i use the facility icon (miner, oil rig, etc.) then an arrow to the right and the icon of the resource being extracted:

[Miner] -> [Iron Ore]

For consumers i do the consumer icon (f.e. smelter) arrow to the smelter and resource icon after that:

[Smelter] <- [Iron Ore]

I also use "in" and "out", in combination with rich text. For example, iron ore stations might be:

[IRON ORE RICH TEXT] 1-4 Iron Ore - Out [IRON ORE RICH TEXT] 1-4 Iron Ore - In

Where the "Out" station is at the resource patch (ore comes out of the ground) and "In" is at the base (ore goes in to the factory). I also include the train type in my station names (1-4).

See https://lemmy.ml/comment/686775 for what I mean by rich text

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

I am usually doing [Station purpose] - [resource] [in/out] E.g. iron ore smelter - iron ore in iron ore smelter - fuel in iron ore smelter - iron plates out (where iron ore and fuels is going INTO the station, and iron plates are going OUT of the station)

Makes it pretty clear, and has never failed me yet.