I hesitate to ask for standard symbols, but is there a de facto standard symbol(s)? Or a popular set of symbols to use for electronic markers?
Our utility will soon start marking with electronic ball markers similar to these:
http://images.pennnet.com/articles/ww/thm/th_193172.jpg (from Water World Article 'Municipality Marks New Pipelines for Future Access').
I found this one somewhere, but I can't remember where I grabbed it from:
Are there others?