I know this is going to cause an uproar but I have an idea on this one. I have been carrying my o2 bottle on top since I started deco which I really like. I have only been doing deco this year so am relatively new to tech diving. It was made clear to me by many on this board that this is not recommended. I am however able to see my bottle fine as I bungee mount the rear clip. However in the name of ensuring my safety and considering the advice of other more experienced divers I explored the following.
Here is what I am experimenting with. The reg has a plastic MOD tag on the second stage. It is permanently attached and clearly indicates the mix/mod on both sides. Mine is 2"x3" although It could be any size. You deploy the second stage. Read the tag, confirm with your buddy and then use the gas. The tag is installed on the surface while everything is clear and there is no chance of a mix up.
If this was an acceptable method then it would so simplify carrying a stage bottle in SM as they ride so nice on top. Comments? Please don't sh$t on me, it's an idea only being considered as a safe alternate. If you read the bottle mod or read the reg mod tag the result should be the same. It may even be a bit safer If you were carrying two mixes as the last piece that goes in your mouth on the delivery system has a tag that says the MOD. The tag is permenently installed on the surface and double checked on the surface with a clear head.
Stano
I do something similar, i have the MOD written around the top of the bottle so I can see it when i grab the reg, turn the bottle on, etc.......I still have the sticker at the bottom for my buddy to see.