Our system automatically records every Seyret installations. When you install Seyret on your site and go to administration page, Seyret will contact to our servers with your installation url. Our server will check this url and will try to find any previous record. If it is a totally new installation, it will create an automatic JH User Id for your installation. Otherwise, it will check your existing licenses etc and will recover your license.
JH user id is a randomly generated string. It has some internal rules to prevent duplicate user ids, but as general it is a random string. It is not your http://www.joomlaholic.com site account user name, or it is not your Joomlaholic forum user name. It is just an identification string to your Joomla installation. Also it is not your user name on http://www.seyretusers.com. Then why do we name it as user id? This may sounds silly at first glance, but we had some other component plans when we put these rules. So we were planning to use this same identity on the the components or extensions. Now we are focused on only Seyret, but as this JH user id is spreaded much and all our users know what it means, no need to change this name and cause conflicts.
JH user id totally depends on the url when you access to Seyret backend. Sometimes, you may have some domain aliases. For example you can access to your site site1.com and also site2.com. These two urls can point to the same installation. However Seyret will consider them as two different sites and assign a different JH user id. If you get a license for this kind of site, please contact us with your details. It has a different pricing and licensing policy, but it will not cause any problems with Seyret.
I suggest you not to share you JH user id on forums, just for your security. Yes people can do nothing with just this user id, however being cautious is better.