Emojis is a major potential example, as shown by the fact that the Unicode standard has been considerably extended to include them. However it’s debatable that these are notations in the sense you mean (technical symbols presumably).
In avant garde music there have indeed been notations invented and to some extent adopted since 1960. Back then it was quite common for composers to devise new notations for obscure techniques etc in their own works, though there were usually existing (often better) ones, albeit not standardised. A 1974 attempt to set standards with a conference in Ghent only partially worked.
The rise of music notation software since the 1990s has increased standardisation, as composers now use such software (rather than pen & manuscript paper), which somewhat constrains what fanciful notations they can use.
Emojis is a major potential example, as shown by the fact that the Unicode standard has been considerably extended to include them. However it’s debatable that these are notations in the sense you mean (technical symbols presumably).
In avant garde music there have indeed been notations invented and to some extent adopted since 1960. Back then it was quite common for composers to devise new notations for obscure techniques etc in their own works, though there were usually existing (often better) ones, albeit not standardised. A 1974 attempt to set standards with a conference in Ghent only partially worked.
The rise of music notation software since the 1990s has increased standardisation, as composers now use such software (rather than pen & manuscript paper), which somewhat constrains what fanciful notations they can use.