system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What's the "secret code" behind all those letters, numbers, and symbols that are spray painted on the street, typically before/after construction?

In general terms, it seems the yellow paint represents gas lines and blue represents water, but I've also seen red (sewer?), white (power?), and green. There's also arrows, numbers (which I assume is depth?), and symbols which I haven't been able to decipher.
gpt
Short version? Depends on who wrote it.

They're basically internal post-it notes between surveyors and construction workers.  They usually contain three-four things to them: Color means the type of line, Then the put down a (usually abbreviated) identifier for the line meaning something like "sewer line #2456," or "Sewer at 4th street & main." That part is completely up to whatever standard the company is using.  Then they'll put down some symbol about the line, typically depth, but also sometimes flow direction, High Voltage/Low Voltage, if there's something important below you....

It's really just depends on who is writing the notes.

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The colors aren't "technically" unified, but these four are almost always the same:

* Blue = clean water
* Yellow = Natural Gas line
* Green = dirty water (sewer, storm overflow)
* Red = Electricity.

Orange (sometimes pink) is typically Telecommunications---cable, fiber optics, internet, phone, etc.

White doesn't mean a whole lot, as it's the "general" color.