"aryamansingh go to your profile, find the link that says "signature" and click on it.
There will be an edit box in that page, in most screen readers you can hit e to go straight to it.
write the signature you want in there. If your signature is too long you will simply not be able to write anymore, also, obviously don't press the enter key too many times to put in line breaks.
when you've written this out and are happy, find the button that says "update profile" (go to button is usually "b" in most screen readers, press that button and your signature will be saved. you'll see it on the front page of your profile, and under your posts if you have viewing of signatures enabled.
hth.
With our dreaming and singing, Ceaseless and sorrowless we! The glory about us clinging Of the glorious futures we see,
Our souls with high music ringing; O men! It must ever be
That we dwell in our dreaming and singing, A little apart from ye. (Arthur O'Shaughnessy 1873.)