try this: 
addEventHandler("onResourceStart",resourceRoot,function() 
    if source~=resource then return end 
    local policeTeam = createTeam ( "Police", 0, 0, 255 ) 
    setTeamFriendlyFire ( policeTeam, false ) 
    local players = getPlayersInTeam ( getTeamFromName ( "Police" ) ) 
    if #players == 0 then return end --ends the script if there's no players on the police team 
    for _, player in ipairs ( players ) do 
        createBlipAttachedTo ( player , 0 , 2 , 0 , 0 , 255 , 255  ) 
    end 
end)