Atop one of the Adobe building towers is a public art piece called the Semaphore. The four slotted circles rotate every few seconds and are actually transmitting a code. The puzzle is for interested code breakers to crack the code. It is currently displaying the third code since going up in 2006. The first two have been cracked and now the third is up since 2023.
Some info about the previous coded messages is here: https://825mph.com/adobe-art-san-jose-semaphore .
By artist Ben Rubin (https://www.earstudio.com).