what is the trade symbol of the government bonds themselves ?

I would like to invest in U.S.A government bonds directly (only govt bond index linked) and without involving securities that are indirectly related to government bonds but only just government directly.

When I were looking for government bonds, all I could find are other kinds of securities such as mutual funds which invest in government bonds and such as ETFs & ETNs which invest in government bonds, but not the government bonds themselves.
I am not interested in any other kinds of securities that are indirectly related to government bonds, but only in buying government bonds themselves.
The bottom line I wanna to know, is what is the trade symbol of the government bonds themselves ?

regards

"trade symbol" i mean Identification Number/Sequence Numberq/security number… ….
then, I would appreciate it if you could write for me Identification Number/Sequence Numberq/security number… ….

regards