If I am walking behind someone who has just littered I often (if my own mother hasn't already) pick up what they have dropped (depending on where it lands on the sanitary scale) and quickly catch up to them loudly expressing in a cheery tone that "ooopsy! You've dropped something"
I find this especially necessary when the littered item is cellophane from cigarette packets... Yes "packets".
One of many excellent contributions from Gerdy this week - the necessity of hand written thank-you notes. People! this is the only way to go! Gerdy knows what she's talking about, I've received one from her...even the envelope was lined with the same glossy black that the "thank you" on the front of the notelet was embossed in... Yes "notelet".