Personally, I prefer seeing just "Bump", instead of a pointless "Foo is winning with a bid of 99k" - pointless because that info should be perfectly obvious from the previous posting. At least just saying "Bump" is honest; not just trying to find an excuse to post something so it's back in 'recent threads'.
I bump, and I do it by saying who is in the lead. After a day or two though, everyone is just ready for the auction to end, including me, so I only bump it for the first day, usually.
For example, please see this one; [AUCTION]silk touch I efficiency II diamond pickaxe So - is that acceptable? Genuine question. As far as I can see, it doesn't break any specific rule; and it's certainly effective. It's also very annoying.