ATTENTION: Testing from within the same network might fail!
It is possible that people from within the same network/internet connection (e.g. 2 PCs connected to the same router, one hosting, other one viewing the serverlist) can't see each other. This does NOT mean, that nobody sees your server! It can be caused by wrong router settings and many other things. It might work perfectly well for everyone outside your network! Please ask someone who is not using the same internect connection to check if he sees your server!

Checklist
An unlisted server can be caused by wrong settings or other problems. Try/check the following:
Maybe the U.S.G.N. is down. Check its status at USGN.de and try again later

Make sure your setting "sv_lan" is set to 0! Execute "sv_lan 0" to change it!

Enter "usgn_info" in the console (or execute with RCon) and see if the U.S.G.N. address is 85.214.102.60
Enter "usgn_addserver" in the console (or execute with RCon) and see if it adds your server to the list
Configurate all firewalls so they don't block messages of the CS2D server
Restart (reboot) your whole server completely (not just the CS2D server program)
Just wait! It might take some time until your server is added*

*) It normally takes just a few seconds until your server is added. Some people report that it takes hours for their servers. We actually don't know why it takes so long for some servers. Please be patient.

Also don't just check the in-game list! Open the server ip list and search for your IP there. Please read "Nobody joins/sees my server" if your IP is listed there but if your server is not visible to others in the in-game list.