Yes Feeding pigeons and even Seagulls is against the law in most places. However you're unlikely to get caught or charged with anything since law enforcement nor any city inspectors have the time or resources to really pursue the people to cite you for feeding the pigeons or seagulls.
If caught and charged however you'll likely just face a fine of $500.00 or less so it's not really that big of a deal and I think it's stupid that it's even a law in the first place.