You need to become an established member to have your signature displayed in posts and gain the ability to edit it - https://forums.digitalpoint.com/help/established You're only 2 likes away. Contribute some good content to Digital Point and you should have those likes in no time. Asking for likes will get you banned, btw. Good luck.
A number of reputation points was converted to likes (I think it was 5 rep points equals 1 like - but I'm not 100% sure). If you have never received any rep points for your posts in the past, you're out of luck. Gaining likes is a lot easier, btw.
No, the number of rep points had nothing to do with it... 1 rep (regardless if it was worth 0 or 10 or anything else) was converted to 1 like.
Have you taken a look at your posts? Not much outside BST and General Chat. I'm not surprised you didn't get rep for them (at least positive, anyway). Focus on quality, not quantity. Engage with others in the community, provide some useful help. Maybe there's something you specialise in and can give people advice on it when they ask for help. It's really not hard at all.