What kind of naming conventions is used for custom directives?

For angular custom directive the best practice is to follow camel casing and that also with atleast two letter’s. In camel case naming convention we start with a small letter, followed by a capital letter for every word.
Some example of camel cases are “loopCounter” , “isValid” and so on.
So when you register a custom directive it should be with camel case format as shown in the below code “companyCopyRight”.

app.directive('companyCopyRight', function ()
{
return
{
        template: '@CopyRight questpond.com '
 };
});

Later when this directive is consumed inside HTML before each capital letter of camel case we need to insert a “-“ as specified in the below code.

<div company-copy-right></div>

If you are making a one letter prefix like “copyright” it’s very much possible that tomorrow if HTML team creates a tag with the same name, it will clash with your custom directive. That’s why angular team recommends camel case which inserts a “-“ in between to avoid further collision with future HTML tag’s.