WowAce

alt-<mainName>
@<mainName>

Example:
alt-Ubermage
@Steve

GuildGreet is unfortunately not using libAlts. The syntax they look for in guild notes is limited to the above format. In GuildGreet, @<name> is used to specify an alias such as a real life name or whatever the player wants to be called. The alt-<main> syntax is used to specify the main. I suggest adding both because doing so allows the users to choose to use the alias when provided or the main depending on guild culture/norms.

Refrerences:
* https://github.com/gOOvER/GuildGreet-Extended
* https://mods.curse.com/addons/wow/guild-greet-extended
* https://wow.curseforge.com/addons/guild-greet-extended/

I use various guild management addons and for Alts addon become compatible with the other addons it was necessary to include more formats.
To include the Alt <name> format I added the following method in Alts.lua file.

[13] = {
	-- Alt <name>
	regex = "[Aa][Ll][Tt][ ]+([%a\128-\255-]+)",
	description = "Alt <name>",
	enabled = true,
},