For example, I usually use
- 560 BCE
- 1066 CE
As opposed to the traditional:
- 560 BC
- AD 1066
Some people, when using AD, place it after the year:
- 1066 AD
How are epochs commonly denoted?
Commonly, BC follows the date and AD precedes the date when referencing a specific year. Wikipedia suggests this is because English copies Latin usage of placing the abbreviation before the year number. Since AD is a latin phrase and BC is not, we arrive at 535 BC and AD 1066. Not the most compelling objective argument, I admit, but entirely plausible considering the other odd constructions we've kept around simply because of Latin tradition.
When referring to a century as a whole in text, the convention of placing either BC or AD after the stated century is considered acceptable by most of the style guides I dug up.
Wikipedia goes further to note that CE and BCE are becoming increasingly common in academic and religious writing, and suggests that CE and AD should not be used unless the date or century would be ambiguous without it.
As an aside, I remember seeing one unusual date-reference acronym that was a good five letters long. It had to do with radiocarbon years, if I recall correctly. The full acronym escapes my memory at the moment, but hopefully someone will read this and chime in.
You should adopt the practices of wherever your writing will end up. If you submit to a paper or journal, check their style guides or ask an editor which they prefer. Schools and their professors will often have a preference and following their lead shows them a few things:
I suggest we all start using Unix Time which is the number of seconds elapsed since midnight Coordinated Universal Time (UTC) of January 1, 1970, not counting leap seconds. So for instance, as I'm writing this it's 1302186003. Battle of Hastings: -28502703439. Here's a red-letter date in the history of science: November 5, 1955 or -446722639.
Going to their meaning:
560 Before Christ
Anno Domini 1066 = In the year of the Lord 1066
Grammatically the only way to place them that makes sense is BC after the year and AD before the year. However, as abbreviations that is not as obvious, so either is still usable in the ‘wrong’ place without causing havoc. “BC 560” can not reasonably be misinterpreted as “Before Christ number 560”.
Seems like this is mainly an issue when you're referring to dates BC/BCE, since if you cite the date "1970", for instance, most people are going to know you mean in the present era, not the ancient one. (That gives me a thought: why not use mathematical signs, + and -, as the designations, so that 2000 BC/BCE would be -2000? Maybe a letter would have to be inserted, such as "Y" or "A", so it would read -A2000, so it could be distinguished from regular mathematical functions.) Anyway, the use of the word "common" in the CE designation doesn't really bother or offend me politically or religiously because of the assumption that it's more "real" or "correct". I put it in perspective with a little humor remembering the other meaning of "common": Vulgar, course, boorish, uncivilized, unrefined, low-class, inferior, etc.