Silco did Do his Shard-ly duty and then absolutely followed around any suspicious looking NPCs. He did not harass them, and may have followed some invisibly -- but he was explicitly looking for suspicious activity. He did, however, peel off when they inevitably went home/met up with friends/did something else to assuage his suspicion.

He also got into a fight with Caitlyn

And participated in two rounds of the boss fight as support until Sebastian threw him into a pro-regent display, and he was out of shimmer anyway!