None exists, or can exist without going through the proper standards bodies, and even then there are major roadblocks. The only real solution I see is for an altogether independent file format to be established for this sort of thing.
The big underlying problem here is that these icon sets are an abuse of the font format. A convenient and practical one, obviously, but still fundamentally wrong. Web developers often use floats to create layout columns. All of the weird bugs and hacks we've had to deal with aren't only due to browser bugs, but also because that's just not what floats were meant to be used for. Similar situation here.
- The lack of a standard you're observing is actually an artifact of the icon designers cheating for the sake of convenience. Picking up on your example, Unicode has a position for a right arrow. That particular glyph even has a convenient named HTML entity. But it's much easier to hit
a on the keyboard than
Alt+2192 so that's what the designers assign it to. The standard you're asking about already exists, partially, except...
- There's a another cheat involved here in that font files aren't even intended to contain some of the information in these icon sets. Unicode is generally intended to represent writing systems. Obviously it's a bit wider than that and contains all sorts of symbols like that right arrow, but I'm pretty sure it's never going to have a glyph that means "sync files" or "PDF."
- Now, there are empty spaces in Unicode that icon designers could theoretically get together and decide will have certain icons in them, but unless they actually went through the Unicode Technical Committee, it would really just be an even further abuse of the font format. If at some future date those glyphs were given official definitions, it could cause all sorts of problems on sites that now need those glyphs to represent language.
- Even if a standard were somehow established, your question pre-supposes–actually kind of requires–a universal set of icons. That's obviously a fantasy. But think about it: If you come up with a standard, it's going to assign a bunch of common icons to the letters a-z, for obvious convenience. Now, let's say I happen to make an icon set of some really esoteric symbols. The standard is going to shunt my icons to some weird key combination. Eventually, people are going to start resorting to the same cheating I described in #1.