You need to get established to be able to add a signature: https://www.digitalpoint.com/help/established
All forums need you to have a certain number of posts, points before you can add a signature. You are new, and do not have enough posts/points, that is why
You must have missed the sticky at the top of the Support & Feedback forum, which answers your question
a signature on this site, is not that important. Users that are not logged in, do not see signatures. Members that are logged in, and know what they are doing, do not see signatures either. Changing the settings, to disable viewing others signatures improves readability of the forum, especially on small, handheld devices.
well its really does not matters to put signature in this forum or not... but i feel to gain trust and self-respect for yourself is important thing which one should look for