Notation for latitude and longitude is easy and people should stop being annoyed by it.

Simply use order (either the lat, lon convention or the lon, lat convention).

If you need cross-linguistic symbols for an equation, use the Greek letters (either the θ = latitude, φ = longitude convention or the θ = longitude, φ = latitude convention).

Personally, I find it clearest to just abbreviate them, so l = longitude and l = latitude.

Lest anyone think I’m making up the Greek letters.

And to be fair, sometimes you also see λ. That’s great because λ is equivalent to l, so it stands for the one of longitude and latitude that starts with l.