This happen to me too allot. It happens wen you flash some zip that is not OK for the device. To fix it flash CWM recovery again via odin.
Signature verification failed is normal. Just wait odin to finish.
For the adb method copy recovery.img to internal sdcard not external, run terminal emulator on phone and type:
dd if=/sdcard/recovery.img of=/dev/block/mmcblk0p13
i am new at this stuff..
i am having same problem can you explain in details...