Is it permissible to smile at a street cleaner with the intention of alleviating his worries?

The fitna (temptation/trial) of women for men is a grave danger. A woman is commanded to conceal her adornment and to avoid everything that incites fitna, such as not speaking in a soft, alluring manner, as Allah Almighty says: "So do not speak in a soft, alluring manner, lest he in whose heart is disease should covet," and not striking their feet [on the ground], as Allah Almighty says: "And let them not strike their feet so as to make known what they conceal of their adornment." Therefore, smiling at a non-mahram man falls under the category of that which incites fitna, and is thus not permissible.