If you have come across this information on the familysearch.org site (Mormons) be aware that the date may be a pure guess on the part of relatives of a deceased person. I have been doing family history for lots of years, and c or circa only seems to appear on this site It is a very good finding aid, but ALL information you gather should be from the original source and checked via another source if at all possible. EG information on someone's marriage certificate may not be correct - it is what was said at the time of marriage - the bride may have said she was older/younger for some reason - therefore her year of birth would be way out if you were looking for her birth certificate. Census information is useful too, but there again open to error - especially from an employer who may have guessed a servant's age or place of birth. Another tip (from bitter experience in the beginning) , make sure you make a note of where you got your source information from - you will remember where you got your information from, but in two years or so you may not?