I don't think there is a standard, but there definitely is some sort of convention. If you see a design with a diode and some sort of marking, then your best bet is that the marked side is a Cathode.

I tend to follow the [Diode Marking Guidelines][1] from Screaming Circuits and place a little diode symbol next to my diodes. Only in very tight layouts I will revert to a "dot" to mark the cathode.


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[![Diode Marking Guidelines][2]][2]


  [1]: https://i.screamingcircuits.com/docs/LED%20markation%20at%20Screaming%20Circuits.pdf
  [2]: https://i.sstatic.net/4v6mE.png