[elric]

I always assumed it originated with Perl, where $ is for scalars and @ for arrays.

[avian]

I'm sure this use of $ character is much older than Perl.

One counter-example I know first hand: Sinclair ROM BASIC uses $ for denoting strings, in both variable and function names.

The one I have in a Spectrum is copyrighted 1982, around 5 years before first Perl was released.

I'm sure there are older examples like this.

[elric]

You're right, seems like this usage goes back to at least 1964 in BASIC.