Craft moved from the golden gate towards the south bay, pen shaped semi translucent grey in color, single blinking white light at tip

large pen shaped craft floating below airplane much lower in altitude, the UAP was proportionately larger than the airplane at a further distance. Crawled at a slow pace moving south, from my vantage point it moved from the golden gate bridge towards the south bay, I lost vision behind a tree. Looked as if I was to hold a pen at arms length in terms of size, physically seemed to be floating across the middle of the bay, between SF and the East Bay