Use this inexpensive tip to expand your addressing options beyond black sharpie or a layer of scotch tape. Because I like using an ink that suits the contents of my envelope or package, and don't care for marking the front of my envelopes with tape, I rub my addresses with beeswax to make sure that they don't smudge or smear in transit.
In these photos I chose Waterman black ink in an Esterbrook with a 9668 nib to address an envelope for business purposes.
In this photo you can see the clear layer of waterproof wax laid down by a quick rubbing:
Blocks of beeswax can be purchased in many different types of stores, I purchased mine in a hardware store where it was being sold as a drawer lubricant. As an alternative, I have also heard of people rubbing with a white candle.