Update 11/26/12 - Updated Lync Server 2013 schema version for RTM.
Update 7/19/12 - Added Lync Server 2013 schema version.
Update 10/6/10 - Added Lync Server 2010 schema version.

Verifying that SchemaPrep completed successfully before turning back on outbound replication on the Schema Master in AD is always a good idea.  Depending on the version OCS/Lync that you are running, there are differeing ways to check the schema state.

OCS 2007/R2

The quickest way is to run the following LCSCmd after running the SchemaPrep step:

LCSCmd.exe /forest /action:CheckSchemaPrepState

If the report shows everything as successful, you can feel confident that everything completed properly.

Lync Server 2010/2013

The best way in Lync Server to check that SchemaPrep completed successfully is to run the Get-CsAdServerSchema cmdlet in Lync Server Management Shell.  If you get the following result back:

SCHEMA_VERSION_STATE_CURRENT

The SchemaPrep step should have completed successfully.

 

But, if you want to go that extra step, you can look in ADSIedit.

In ADSIedit, under the Schema Container, look for the ms-RTC-SIP-SchemaVersion.  Opening the properties, look for the "RangeUpper" attribute.  Check the list before for the correct value for your environment:

LCS 2005 - 1006
OCS 2007 R1 - 1007
OCS 2007 R2 - 1008
Lync Server 2010 - 1100
Lync Server 2013 - 1150

If you see the correct value for your environment, you can be sure that schema prep completed successfully.