The K inside a circle indicates that the food has the “OK” Kosher Certification (the OK), which was founded in 1935 under the leadership of kosher food pioneer Rabbi Berel Levy, has become one of the world’s most respected symbols of kosher approval. Foods labeled with the OU symbol or U within a circle means it has been certified by the Orthodox Union and it is one of the strictest kosher standards. There are also other kosher labels.
Guide to Popular Kosher Symbols
There are reasons to certify foods beyond meats as being kosher such as a food coloring derived from shellfish or insects, certain foods that contain tallow, gelatins or casein, dairy products such as cheese that contain animal fats.
You've probably consumed many, many food products that have some type of kosher certification and never knew it.
Many Muslims FWIW will look for the kosher certification label on foods because Halah dietary laws are very similar.
The Halah certification label is an M inside a circle or this label:
The R on product labels means it, the product name or logo is a Registered Trademark and has nothing to do with being either Kosher or Halah.