It can be the no deposit, 1st deposit, or free spins bonus that you can use for a specific slot or for all of the games in the casino, which is quite rare.
http://users.atw.hu/tunedthings/viewtopic.php?p=335931#335931
https://talk.hyipinvest.net/threads/277285/
http://www.pravoslit.ru/forum/obshchee/324212-juegos-de-apostar-dinero-real-o-mejores-casinos-online-en-per.html
https://mmomakemoneyonline.net/threads/gry-na-prawdziwe-pieniadze-online-oraz-automaty-na-prawdziwe-pieniadze.409229/
https://mmomakemoneyonline.net/threads/slot-online-argentina-casino-online-chile-paypal.537600/
http://www.prepody.ru/topic88249.html
https://www.ww2.site/forum/viewtopic.php?t=78210
http://forum.bandingklub.cz/viewtopic.php?f=17&t=1298380
http://forum3.bandingklub.cz/viewtopic.php?f=15&t=1196650
http://ewmen.com/viewtopic.php?t=579083
https://debate.socialism.nl/forum/showthread.php?tid=117765
https://www.ww2.site/forum/viewtopic.php?p=345904#p345904
https://www.ww2.site/forum/viewtopic.php?t=173862
http://users.atw.hu/tunedthings/viewtopic.php?p=330695#330695
http://forum3.bandingklub.cz/viewtopic.php?f=40&t=1078904
http://forums.shlock.co.uk/viewtopic.php?f=2&t=437133
http://881.cz/forum.php?mod=viewthread&tid=30292&extra=
https://www.ww2.site/forum/viewtopic.php?t=40335
http://horsecity.ru/phpBB3/viewtopic.php?f=14&t=160989
https://debate.socialism.nl/forum/showthread.php?tid=164621
http://forum.ruchkontroliwyborow.pl/index.php?topic=22334.new#new