Ok just to be difficult I want to put forward some issues
1. Let's say that a quarry of default size at least always keep 4 chunks loaded. Point out that I know what I'm doing and can resize the quarry to always keep 4 chunks loaded but with a size that is larger than the custom size, would this be acceptable? My reasoning is that the size shouldn't matter, only the number of chunks loaded. In worst case you might even end up loading more chunks with a badly placed default sized quarry than a well placed custom sized one. I haven't tested this myself, but apparently you should be able to display chunk boundaries on the minimap.
2. I hope you don't have to baby-sit your quarry in case it happens to dig into water? It should be enough to just check that before leaving right?
3. Again I haven't tested if this exists on our sever, but apparently railcraft has a magnifying glass item that you can craft. This is supposed to show you who has placed a block, and if this is the case the signs shouldn't strictly speaking be needed.