The question is, can we really stop people from shilling, I think it's hard to do that as it's not against the rules (correct me if I am wrong).
If you are shilling for a scam, then it is obviously against the rules. I am not doing a good digging as far as this Titan Coin is concerned but if the coin is not a scam, then shilling for it is all right for as long as it does not go as far as it is annoying and off topic. Shilling is just another term for promoting or marketing, although it has a little bit dirty connotation.
I think it still depends on the quality of the post before it can be considered as violation of the forum rules. If the the two shill accounts mentioned in the OP merely posted links of the titan website and no other contribution, it will be deleted for being low value. If they posted some referral link or phishing site, that's also a violation.
Not just the quality of the post. If the post is highly informative and even very detailed in its presentation but the content is all about the promotion of a scam or a ponzi, it will have to be taken down.
"Scam coin" is also subjective here. If you visit the scam accusation board, you can see plenty of ponzi schemes and projects with fake team or plagiarized whitepaper being flagged/tagged by the community but their ANNS aren't being deleted by mods.
There must be objective and exact parameters when calling a coin scam. Sadly, though, in this forum, scam is not moderated nor regulated. There is no one who is assigned to scrutinize every single project coming in whether or not it is a scam. And, yes, scam is now a word which is fast becoming subjective, when it should not be.