The reason to save SHSH blobs, you will be secure to downgrade your device to the previous firmware version which can be jailbroken. So its better to save your iDevice SHSH blobs, because you wouldn’t be able to save old SHSH blobs if Apple releases then new version of firmware. If you want to save SHSH blobs (ECID SHSH) for iPhone, iPod Touch and iPad device then follow this guide to save SHSH blobs now.
Check this new guide: Save SHSH Blobs. Below is an older version guide.
Make Sure you have of iTunes 9.0 or later version installed.
Download latest version of TinyUmbrella for Windows.
Run TinyUmberalla and plug in iPhone / iPod Touch / iPad into your system using the data cable.
When TinyUmbrella recognized the connected device, click on “Save My SHSH” button. This action will grab the signature.
You are done!
This will save a copy on your computer and also send a request to Cydia to save your SHSH on Saurik’s server.