To elaborate more on the topic.
As some of you may or may not know, not all Kodak photo paper is branded with the same watermark on the back. Knowledge of the different types of watermarks and the time period in which they were used can be useful to those who collect vintage photos. For example, if someone was trying to sell you a colored photo of Marilyn Monroe, which you were told was printed in 1961 on Kodak photo paper, and when you turned it around you saw
You should be hesitant to trust them because from 1961 – 1972 Kodak marked their colored photo paper with,
A KODAK® PAPER
Before that time they were marked with “EKC” encircled by a double-lined circle.
In 1972 and up until the early 1990s they changed the mark to,
Now, trying to determine a more exact date for photos printed during this 20 year or so time period can be tricky. During this time period Kodak also used selective underlining of letters and in the 1980s they also introduced selective overlining of characters. So, if you have a photo with this watermark and some of the letters have an overline you know that the photo could have been printed no earlier than 1980. However, I am not sure if all Kodak colored paper had overlines in their watermarks during the 1980s or if only some.
What I am hoping is that someone here with more knowledge of Kodak’s branding scheme can help me narrow down the possible age of these photos a little more.
To finish up, in 1989 Kodak started to brand each of their individual product lines with a unique backprint/watermark.