As ThisIsMe said it's the new secure trade gump in the Time of Legends expansion.
I suspect there's additional data that needs to be included in SendSecureTrade (or whatever its called) gump packet.
When it comes to packets and packet building I know even less about that than I do about advanced computer programming which means I know nothing about building packets.
I don't play the "pay for" official servers so someone who does will need to do some "packet sniffing" to get the info being sent to the client. I will tell you I didn't have that gump pic in my gumps UOP file because I was using a custom gump.mul file rather than the one that came with ToL and when I initiated a secure trade no gump appeared. So that tells me that they are using the new gump now.