Subscribe to individual threads?

Good morning. I know I can grab the RSS for the forums, but what about subscribing to individual threads.

I've participated in several forums where there is a toggle in your account profile that allows you to note a desire to be emailed once you post to a particular thread. I'm following a couple of threads right now, and have been through all the fields (I think) of my account and can't find a means to "subscribe" to threads I've participated in.

Thank you for any assistance.