Your signature Information is stored locally and Outlook does not stored it in the server hence each time you access your Outlook on different machine you need to provide signature info.

I found a workaround for your problem in this blog. Please see if that helps.


*Extra info*
The default folder where Outlook email signature files are located is:

Windows XP: C:\Documents and Settings\%username%\Application Data\Microsoft\Signatures

Windows 8 / 7 / Vista: C:\Users\%username%\AppData\Roaming\Microsoft\Sign atures