AFAIK the symbol for ultrabond futures is OUB or OUL. OB is the symbol for Euro/Krone. You are reading too much into this. It can be anything, any of the thousands of strategies for arbitrage or hedging. My advise to you: stay clear. These people are sophisticated in ways you cannot imagine. Don't ever try to mess with them. You are a drop in the bucket for them. Just forget about what you think you have seen and move ahead. You will never make money out of these people and even if you manage you may get into trouble.
I think it is very sound advice generally speaking. But on specific cases, it might be possible to make money off algos. To OP - From your pictures, it seems there is merit in what you have seen. So there is a clear autocorrelation at least as far as having same volume getting transacted on same side is concerned at some time of the day. It seems to me (haven't really done much thinking on this) that you might be able to make some money off this phenomena by going in direction of this volume as soon as you see this, and then getting out of the trade after price moves 1-2-3 tick in your favor (this will depend on how much price this algo is able to move). If my understanding is not too off, I suggest you to start doing this from Monday with 1-2-3 lots and after seeing how you perform for a week or so increase size. Good Luck!
This is bank order desks running algos to place end of day trades for their CTA, hedge fund and other institutional customers. The bank order desks get jammed late in the session with multiple customers calling and submitting large orders with instructions to capture the closing price. And I wouldn't recommend trying to 'get in front this'. Perhaps they start of with buy side algo 1:00 in to the close and follow up with sell algos, for other customers, :30 before the close? They can effectively drive the price up for one customer so the the other customer and sell into that better prices.
If you know flow is comming, you can front run it. Nothing wrong with that if based on public information.
A market observer has no way of knowing the flow is coming. You don't know how many contracts comprise the entire order. You don't know if the bank trader is setting up for a contra-trade of even greater size. Best of luck trying to get infront of these. I'd love to see your results.