I've done a lot of research on spam checker signatures in Marketo. The good news is that there are certain signatures that will key you in that a spam checker is in action. For the most part, you will see them consistently occurring for leads in the same company ( corporate email often using a specific spam checking configuration).
There isn't a simple answer to your question though. First, it depends upon how you capture your "numbers". If you are relying on Marketo stats for email opens, links clicked, etc., then you are stuck with the way that Marketo captures this information. Marketo doesn't filter out spam checker signatures in its stats.
However, if you control the stats (which is how I usually set up email programs in Marketo) by setting program statuses and getting your email stats through the program statuses instead, then there is some hope. By setting the program statuses through smart campaigns, you can use triggers and filters to weed out the spurious activities that spam checkers are creating. It won't be perfect - meaning that you may lose some real activities. But it is a potential solution. When I was researching this, I was pretty sure that Marketo was rich enough with triggers and filters that I could separate out the signature that I was seeing.
I've seen at least 3 different spam checker signatures. But I haven't actually gone so far as implementing the trigger/filter scenario I mentioned above. Instead, I have chosen to take the route where you design the really important activities with spam checkers in mind. (I generally tell my clients to ignore opens and link clicks stats. They are fine for looking at trends and generally o.k. for comparisons - if your emails tend to go out to the same representative sample of your database. But for activity tracking, I don't like to rely on them.)
This first came up when I implemented CASL and used a link click in an email verification email to show that someone had verified their email address. That was when I was seeing spam checkers trigger link clicks activities in Marketo and not only link clicks but web page visits as well! How do you combat something like that? Many people thought they could get around the spam check link clicks by adding a web page visit filter. Not so for some spam checkers.
So, for important activities when I really need to know that a person took action from the email, I put the action behind a form completion (prefill enabled). It is an extra set of clicks and I know that I will be losing people's interest for the indirectness of the flow. But for things like email verification and opt-in/opt-out, in this day and age you really don't want to rely on something that could be just as easily triggered by a spam checker as a person.
I'll be at this week's user group meeting if you and others would like to discuss this in more detail.
We have the same issue with a few verticals, and generally in waves a large number of leads within the same company. One thing that we've been trying to do, but is slow due to moving away from HubSpot for our site, is use the trigger visited page instead of clicked link. If that page is a Marketo page or one on our site, that is a way we've found to eliminate those false clicks. It's worth doing some testing and see if that can be of help as well!
I won't be at this months MUG meeting but hope to see you there in the near future!