Hi:
I think you may have misread that sabertooth mark you referred to. I would recommend that you look at it again and reassess your thinking. More importantly, you may want to consult with an attorney -- not a public board -- regarding your issues. You don't want to invest a lot of money in this mark until you've sought the advice of counsel.
You are right to investigate. The Trademark Office will reject a mark if your mark is likely to be confused by consumers with another existing mark. Basically, "likelihood of confusion" means that consumers are likely to be confused by the use of similar marks on related goods and services, such that consumers mistakenly think that all the goods and services are coming from the same company, when they're really not.
There are a lot of factors that go into this analysis, but let me give you a very basic example. Let's say you use the brand name "TEE MARQEE" for your t-shirts and there's another company that uses "T.MARKEY" for their hats. That's likely a problem. Because the marks are similar in sound and hats and t-shirts are often produced by the same company (meaning those goods are related), there's a likelihood of confusion.
Remember: same or similar mark; related goods and services. So, in this case, when consumers hear "T.MARKEY," they're going to assume that both the hats and the t-shirts are coming from the same company. If you want to know all the factors, not simplified as I've done here, you will need to consult with an attorney.