TL;DR
All in-game alerts should be exposed as virtual signals.What?
- Minimalistic approach: Export only signals currenrtly-existing as alerts
- Full approach: Export those signals with different color styles (i.e., red/yellow/blue)
- Entity destroyed (red cross)
- Entity under attack (red exclamation mark)
- Not enough construction robots (yellow robot)
- No materials for construction (yellow gear)
- Not enough repair packs (yellow wrench)
- Platform tile building blocked, Turret fire (yellow exclamation mark)
- Turret out of ammo (red bullets)
- No storage, No platform storage (yellow chest)
- Train out of fuel (red canister)
- Train no path (orange question mark with arrows)
- Collector path blocked (red claw)
- Unclaimed cargo (yellow cargo pod)
- No roboport storage (yellow roboport)
- Pipeline overextended (red droplet)
- Entity frozen (blue snowflake)
- Train destination full (blue Zzzzz)
- Miner out of resources (red drill)
- Entity unpowered (yellow plug)
- Entity out-of-power (red lightning)
- Entity out-of-fuel (red canister)
Why?
126636: Version 2.0.34 added multiple new virtual signals: However, from all alerts the game gives you, only

See also:
Edit:Edit 2025-02-26: Added non-alert alert signs descriptions