There is a common custom to fill the havdalah cup with wine all the way to the brim for the ceremony marking the end of Shabbat, so that a little spills and overflows when you pick up the cup. The symbolism of the custom is that we wish for a week with an overflowing abundance of blessing.
Some communities also dip their fingers in the spilled wine and dab a little on various parts of their body and clothing. Some place wine on their eyes, enacting the verse from Psalm 19:9: "The mitzvot of God light up our eyes." Others touch the wine to their foreheads, expressing a wish for wisdom, their pockets for wealth (some say for fertility), or the back of their necks (not sure of the reason for this one).
The practice of spilling wine and placing some in the eyes as an expression of love for the mitzvah appears in the Rema (16th-century Poland) Orach Chaim 296:1.