Marketo doesn't really have the notion of blind form submits directly from email, but you could always just trigger the alert based on which link they click, then use trigger tokens to alert the rep of which one it was. We do something similar to let our reps know when someone opens or clicks their emails. The alert looks like this:
This person has just clicked a link in one of your sales emails!
{{SP_Send_Alert_Info:default=edit me}}
{{lead.Email Address:default=edit me}}
Email: {{trigger.Name}}
Link: {{trigger.link}}