As has already been said - it is there on all your posts for other people to click on. You cannot rate your own posts so you cannot see it. Adding it to your signature would be pointless and repetitious.
It is disabled in some sections of the forum such as "About EDAboard" and it is disabled for the first post, but I must admit I don't know why it is disabled on "Other Engineering". It is disabled on "Education", probably because the education section is for discussion rather than "help". There is an argument for scrapping the "helped" system which has been discussed before as it seems to be abused by some people. If it didn't exist, no one could abuse it!