Why is the postbit_signature_start hook not listed in plugins?

[BirdOPrey5]

I thought I'd be well on my way to coding my first 'installable product' mod by now but I am foiled before I've even written one line of code.

The most suitable place for my code is the hook called "postbit_signature_start" but this hook is not listed in the drop down list to add a new plugin too... so how do I use it? Is it not listed because it's a template hook as opposed to a php file hook? Surely there is some way of putting code in there?

I feel I'm missing something very obvious.

--------------- Added [DATE]1279589631[/DATE] at [TIME]1279589631[/TIME] ---------------

OK Nevermind- I figured it out... had to use postbit_display_start and call the template from there... as explained here: https://vborg.vbsupport.ru/showthread.php?t=147447