When clicking on an Android signature field, even with orientation lock enabled, the screen rotates to force you to sign in landscape. This works well.

In iOS, there is no auto rotate. To sign in landscape you have to have orientation unlocked, rotate your device landscape to sign, and stay landscape to click save. If you rotate back to portrait then click save then your signature gets squashed. If you sign in landscape but phone is locked to portrait, then your signature is sideways.

Android signatures are fool proof, yet I've had to explain the best way to enter signatures to each iOS user.