Signature

I have 2 emails and I use outlook 2010 and both emails are connected with office 365 exchange on line . Ihave seperate license for each email and both mail boxes sync with exchange on line.

I need to creat a signature for my emails and I was wondering if i need to creat the signature in the on line access or in my outlook on the disktop or in both knowing that I will want to use same signature for all mail boxes.

thanks