Go to the web scripts page (/service/index) in either the platform or Share. The version is shown at the top of the page (see attached screenshot) but it is incorrect.
At the time of writing the version is 5.1.2-SNAPSHOT but it's reported as 5.1.0 (Release).
These values are hardcoded in $SVN_ROOT/services/surf-webscripts/trunk/pom.xml.
There is also a schema version reported, is this even applicable anymore? I presume this was originally showing the platform schema number but this can be found via the admin console now. Furthermore, the schema number doesn't have any relevance in Share.