Here is a neat script to get rules for all your users. It is handy if you are checking for any sig
$Mailboxes = Get-Mailbox -ResultSize unlimited
foreach ($Mailbox in $Mailboxes){
Get-InboxRule -mailbox $Mailbox.Name | fl Name,Description > c:\temp\$Mailbox.txt}
This generates a file per mailbox in c:\temp and if file is 0 bytes, there are no rules.