I would find it intrusive. People in deep grief don't even want strangers looking at them, much less coming up and handing them flowers. When you're standing by a loved one's grave you don't exactly want anyone observing your emotion.

It might be good to reconsider this community service project. If the idea is to spread around some random acts of kindness the first goal would be to act kindly. It's not kind to intrude on someone's deeply personal moment of loss and sorrow.

It would be better to hand out flowers, minus the note, at the entrance or exit of the cemetery. Or better yet, hand out flowers to random residents of nursing homes and assisted living facilities. Or new socks and dollar bills to homeless people on skid row. Leave people visiting the graves of loved ones alone in their silent prayer, meditation and communication.