Prompt is an command that sends the specified message or a blank line to the user's screen.
You can control its behaviour with the TERM system variable
PRO[MPT] [text]
The PROMPT command suppress the spaces at the beginning of the text
PROMPT Nico
will return
Nico
and not
Nico
One solution is to use the DBMS_OUTPUT.PUT_LINE function.
SET SERVEROUTPUT ON
SET FEEDBACK OFF
exec DBMS_OUTPUT.PUT_LINE( ' Nico')