I do not know the right name for a "couillard" in English, and maybe a better 
term will be not as evocative as in French, but the thing is easy to 
understand. For example an asterism ⁂ is probably the most common kind 
of couillard.

                  * *

What should be a good practice to encode them ? This separator is not 
only an ornament but usually a logical separator between groups of 
paragraphs, so the separator should be kept (but the figure could be 
modified for a non imitative edition). The fast and easy way is to 
encode it as a common paragraph.

<p rend="center"> *
* *</p>

Is there better ?

Frédéric Glorieux