I am trying to run unsigned application on iOS 5.1/iPhone 4s (jailbroken). What I did:
Disable code signing in XCode.
Built unsigned iPhone
Starting from what seems Xcode 4.5 onward, maybe as early as 4.4 have not checked, in order to pseudo code sign using the ldid tool, you need to download and install 'Command Line Tools' from here or you can download it from within Xcode, Preferences->Downloads
Otherwise you will get errors like
You still need to make sure it is not a "fat" binary and only armv7 as armv6 is no longer supported.
ldid -S ExampleApp