From W3C Wiki
This page intents to collect topics for good practices in the linked data publishing and discovery process (triggered by a discussion on LOD public mailing list).
Good Practices Collection for LOD publishing and discovery
SPARQL end points can be declared&searched using Apple's Bonjour protocol: SPARQL discovery
sparql, wkl, and http headers
WKL (Well Known Location) is practical but a bad practice usually because it clutters the information space with magic values with sometimes nasty side effects.
Think for example about favicon.ico which creates plenty of 404 requests if you do not have one.
Imagine also that someone had historically a section on his/her web site dedicated to sparql documentation called /sparql Suddenly this not usable anymore for an Endpoint.
There is no useful syntax in robots.txt to achieve it too.
Maybe one possibility would be to use an HTTP header to advertise it.