Symbols that food is kosher
Kosher means "meeting all halachic (Jewish law) requirements." While the word kosher can refer to any aspect of life---even people---it's most commonly associated with food.
To be declared kosher, according to Rabbi Joseph Grunblatt's article, "Thinking Kosher", food must follow specific preparation rules that include how the food is processed (meat and dairy cannot be mixed), where the food originated (pork is forbidden) and time (including disposal of food at designated holidays). Just because a product is labelled "natural" does not mean it's kosher because some oils use parts of animals or are produced on the same equipment.
There are more than 80 kosher symbols in the United States. Each represents a kosher certification organisation that checks food manufacturers to ensure they follow halachic requirement, then sends a letter of certification permitting the manufacturers to advertise that their products are kosher.
O/U, O/K, Kof-K and Star-K are the most recognised kosher agencies worldwide. Their symbols serve as a guarantee to customers that products are kosher, and therefore safe to eat under Jewish law.
Union of Orthodox Jewish Congregations
The symbol for the Union of Orthodox Jewish Congregations, or O/U, is a capital U inside a circle.
The O/U certifies more than 500,000 products throughout the world---including Coca-Cola, Cargill and Procter & Gamble---making it the most recognisable kosher symbol in the world.
The Organized Kashrus Laboratories
The symbol for The Organized Kashrus Laboratories, or O/K, is a capital K inside a circle.
The OK certifies more than 114,000 products worldwide, including Kraft, ConAgra and the Miller Brewing Company. OK's TRACK (Tracking Researching and Certifying Kosher) system---a database of more than 100,000 products---has made it a leader in kosher technology.
KOF-K Kosher Supervision
The symbol for the KOF-K Kosher Supervision is a hollowed out Jewish symbol with a small capital K in the centre.
KOF-K certifies companies throughout the world and was the first Kashrus organisation to track ingredients and suppliers in a database accessible to customers and KOF-K certified companies.
Star-K Certification and Quality Assurance International
The symbol for Star-K Certification and Quality Assurance International is a capital K inside a five-point star.
Due to the growing international demand for both kosher and organic food, Star-K certifies that food is both kosher and organic. The Star-K symbol serves as a guarantee that products not only meet kosher standards, they are also the highest quality.
In addition to symbols, there are other Kashrus (Jewish dietary laws) designations.
D: Dairy DE: Dairy Equipment (does not contain dairy but still cannot be eaten with meat) P: Passover (meets kosher standards year-round, including for Passover) Pareve: Non-dairy and non-meat Chalav Yisrael: Contains kosher-supervised milk Pas Yisrael: Jewish baked goods Yashan: Not from current grain crop