How do I analyze this UART signal?
Try 10500 baud. The data stream should be 0xAA 0x24 0x00 0x00 0x55. My suggestion to determine the baud rate is to look for characteristic bytes. In your capture the long zero sequence is a good candidate (generally, the 0x00 and 0xFF bytes look very characteristic on serial):

10 bits divided by the total length of the marked box gives you the baud rate.