This report will show how many computers the user is currently logged into, This will be the best way to determine if the user has more than 1 pc.
Select Top 1000000 tsysOS.Image As icon,
  tblAssets.AssetID,
  tblAssets.AssetName,
  tblAssetCustom.Model,
  Case When (TsysChassisTypes.ChassisName Like '%Docking Station%' Or
    TsysChassisTypes.ChassisName Like '%Notebook%' Or
    TsysChassisTypes.ChassisName Like '%Laptop%' Or
    TsysChassisTypes.ChassisName Like '%Portable%') Then 'Laptop'
    When (TsysChassisTypes.ChassisName Like '%Mini Tower%' Or
    TsysChassisTypes.ChassisName Like '%Space-Saving%' Or
    TsysChassisTypes.ChassisName Like '%Desktop%' Or
    TsysChassisTypes.ChassisName Like '%Tower%') Then 'Desktop' Else 'Unknown'
  End As [Chassis Type],
  tblAssets.Username,
  tblAssetCustom.Warrantydate As [Warranty Expiration],
  LastUserOn.AssetCount As Computers
From tblAssets
  Inner Join tblAssetCustom On tblAssets.AssetID = tblAssetCustom.AssetID
  Inner Join tsysAssetTypes On tsysAssetTypes.AssetType = tblAssets.Assettype
  Inner Join tblSystemEnclosure
    On tblAssets.AssetID = tblSystemEnclosure.AssetID
  Inner Join TsysChassisTypes On TsysChassisTypes.Chassistype =
    tblSystemEnclosure.ChassisTypes
  Left Join tsysIPLocations On tblAssets.LocationID = tsysIPLocations.LocationID
  Inner Join tsysOS On tblAssets.OScode = tsysOS.OScode
  Left Join (Select a.Userdomain,
    a.Username,
    Count(*) As AssetCount
  From tblAssets As a
  Group By a.Userdomain,
    a.Username) As LastUserOn On LastUserOn.Userdomain = tblAssets.Userdomain
    And LastUserOn.Username = tblAssets.Username
Where tblAssetCustom.Warrantydate <= '12/31/2017' And
  TsysChassisTypes.ChassisName Not Like '%Rack%' And
  TsysChassisTypes.ChassisName Not Like '%Main%' And tblAssetCustom.State = 1
Order By TsysChassisTypes.ChassisName,
  tblAssets.AssetName