Welcome message for oracle schema
HOWTO configure the banner

In the sqlnet.ora file on the server, set the values for:


SEC_USER_AUDIT_ACTION_BANNER
SEC_USER_UNAUTHORIZED_ACCESS_BANNER


You may have to restart the database for the changes to take affect.

Application Requirements

The application must:


use the OCI driver
fetch the banner (using OCI calls)
display the banner


  Oracle Call Interface (OCI) applications can make use of OCI features to retrieve this banner and display it to the user. 



The quote is from Oracle Documentation.

Servers cannot force clients to do something.

Will it work with ...?


SQL Plus - Yes.  See Sam's post
SQL Developer - Yes.  See Sam's post
PLSQL Developer - unknown.  You'll have to use the OCI driver and try it.
TOAD - unknown.  You'll have to use the OCI driver and try it.