I use semitransparent fiberglass-reinforced packing tape to make labels for electrical circuits, phone lines, computer cables and other items that need to be identified during the course of construction. As shown in the drawing, I use a felt-tip marker to put the information on the sticky side of the tape. This kind of marker writes nicely on a sticky surface. In a pinch, a ball-point pen or pencil can make do.
Once the tape is marked, I wrap it around the object to be identified, bring the two sticky surfaces together and cut off the ends simultaneously so that no sticky surfaces remain exposed. When the ends are pressed together, the tape becomes transparent, and the writing shows through clearly. Encased between the layers of tape, the label is waterproof and easy to clean if it gets dirty. The fiberglass tape is almost indestructible, yet pretty flexible, allowing wires with these labels to be pulled through holes in framing or conduit with a minimum of snagging. The labels may become crumpled in the process, but once they're straightened out, the notation will be perfectly legible.
Al Lemke, Hopewell Junction, NY