@markus Something like this may also work:

<#if companyInformation.companyId?contains('_SB')> Sandbox <#elseif companyInformation.companyId?ends_with('_RP')> Preview <#else> Production </#if>

However, if you are also using Developer Accounts (Developer Sandboxes) they will be detected as production, as they don't have a suffix on the account id.