Method 2 (a little more involved, but not dependent on client side Rcon tools to run)

From evenbalance.com:

PB_SV_Task [X] [Y] [command]
Adds a task to PB's Task List; The Task will be executed X seconds after entry and every Y seconds thereafter; use -1 for Y if a one-time task is desired; this can be used to execute game server commands as well as PB commands

Create a file called (just an example, you can call it anything you want) svrmsgs.cfg. Add this text to it and edit for your needs using the explanation above from evenbalance.com:

CODE:
pb_sv_taskempty

// Task setup for PunkBuster

//where <color> =  
//^1 for Red
//^2 for Green
//^3 for Yellow
//^4 for Blue
//^5 for Cyan
//^6 for pink/Magenta
//^7 for White
//^8 for Black

//where <message> = the text you want to scroll

pb_sv_task 10 1000 "say <color><message1>"      
pb_sv_task 100 1100 "say <color><message2>"  
pb_sv_task 200 1200 "say <color><message3>"
pb_sv_task 300 1300 "say <color><message4>"
pb_sv_task 400 1400 "say <color><message5>"



Then upload the svrmsgs.cfg file to your pb directory on the server, and edit your pbsv.cfg file to call the svrmsgs.com by adding "pb_sv_load svrmsgs.cfg"

Finally, do a pb_sv_restart and you should see your messages start to scroll after the first X value of seconds has passed.