A variety of free guides, including a pipe marking guide
There is a new free guide site available online at:

Industrial Safety Guides

They have a pipe marking guide and other useful guides for OSHA and ANSI compliance, GHS and more. The original link to the free pipe marking guide is below.

Pipe marking requires specific colors and text to be in compliance with standards. Various materials require different types of labels. We can help you learn how to properly label your pipes for the following materials and more:

Ammonia pipe marking

Steam pipe marking

Liquid mixture pipe marking

Flow direction labeling

Low temperature recirculated liquid (LTRL)

Low stage suction pipe marking

Thermosyphon supply pipe marking

Link to a free pipe marking guide