Do you have a mobile phone with Windows MObile? If yes, just visit OWA from IE of Windows mobile and delete the original signature.
If there is no such mobile phone, another way is to install a mobile phone simulator.
/downloads/details.aspx？ FamilyID = 38 c 46 aa 8- 1dd 7-426 f-a 9 13-4f 370 a65a 582 & amp； DisplayLang=en
Configure the network and connect to the local computer. Visit OWA and delete the original signature.
Good luck!