>I think I read somewhere that, depending on the exact date, it can return a name that starts with a digit, making it unsuitable for some purposes.

The SYS(3) returns the number of miliseconds since midnight as a string.

? INT(Seconds()*1000), Sys(3)

>You might consider sys(2015) as an alternative. That one returns 10 characters, but I am not so sure about whether it may start with digits, or not. I think it is safer in the sense that sys(3) might return the same name twice, if it is called in rapid succession (twice in the same milisecond or so).

The value returned by sys(2015) always starts with "_" (underscore). The rest could be any alpha-numeric character depending on the current date. See Convert SYS(2015) value back File #9704 for details.