I researched these markings before, but it's been awhile, and I don't save the info once I dispose of the tool. But I do recall it took quite some time to nail it (requiring obsessive persistence). It's a bit confusing and obscure. Here's my recollections.
See the attached photos. Examples of the GUARANTEED forging in the diamond-oblong recess can be found bearing a stamped logo for Atlas Tool Co (see my 2nd photo). But Atlas did not make these. After much research, I traced the wrench to the Erie Tool Works. A 1921 ad at this link shows examples of their goods with the GUARANTEED slogan. You can even see the GUARANTEED cartouche in the illustrations.
https://books.google.com/books?id=P...=bookclip#v=onepage&q=erie tool works&f=false
If you also perform a google search on "erie tool works diamond e" and click on the Images link, you will find similar examples.
On the wrench in my photos, the recess on the dynamic jaw shows the diamond-E of ETW. I lucked out on this because some of these wrenches only have various shapes of recesses with no markings inside. Erie did a lot of contract work for other mfrs and retail chains, which resulted in some ambiguous and misleading marks. But I'm confident that any wrench bearing the GUARANTEED diamond-oblong cartouche is an Eire Tool forging regardless to any of the other markings.
As for dating, the info is kind of sketchy. Based on the few available ads, doesn't look as if the GUARANTEED slogan was used in the 1900s, but was in use by 1921. Because it has no wood handle, and the metal handle of yours looks different than the ad illustration, I'd guess later, 1930s or 1940s for your pipe wrench. If we can determine when the GUARANTEED cartouche was discontinued, that might narrow it down.
Anyway, these are my recollections on the wrench.
EDIT: Look at this too, especially the ads in the margins.
http://www.lakeviewforge.com/about-us/company-history.html