A smile

A smile costs nothing but gives much. It enriches those who
receive, without making poorer those who give. It takes but a
moment, but the memory of it sometimes lasts forever. None is so
rich or mighty that he can get along without it, and none is so
poor but that he can be made rich by it.

A smile creates happiness in the home, fosters Good Will in
business, and is the countersign of friendship. It brings rest
to the weary, cheer to the discouraged, sunshine to the sad; and
it is Nature's best antidote for trouble.

Yet, it cannot be bought, begged, borrowed, or stolen, for it is
something that is of no value to anyone until it is given away.
Some people are too tired to give you a smile. Give them one of
yours, as none needs a smile so much as he who has no more to
give.

-- Author Unknown