Add the following to your user page: {{User:Xenocidic/UBX/Xbox Live}}
{{User:Xenocidic/UBX/Xbox Live}}
If you want your gamertag to be displayed, the first variable should be your gamertag - {{User:Xenocidic/UBX/Xbox Live|gamertag}}
{{User:Xenocidic/UBX/Xbox Live|gamertag}}