Can you disable the Ctrl-S (XOFF) keystroke in Putty?

Don't know about Putty, but you can use:

stty -ixon

on remote host, to disable START/STOP signals.

The PuTTY solution:

1. before creating the session go navigate to Connection->SSH->TTY in the list.
2. in the "Mode" dropdown box, select IXON (nb: as of version 0.60, this list is not alphabetically ordered)
3. put "0" (zero) as the value of IXON.

Works as a charm, even if you open up a "GNU screen" on top of it, SSH to another host, or "su" to another user

If you're using GNU Bash, ctrl-S should allow you now to do a forward-search-history (aka: i-search)

You can see the difference in the output of "stty -a | grep -o ".ixon": With putty configured it prints "-ixon", without " ixon"

.bashrc example:
#
# Stop Putty from doing XOFF/XON with Ctrl-S/Ctrl-Q
# SOURCE: http://raamdev.com/recovering-from-ctrls-in-putty (Morgy, 7/14/08)
#
# stty ixany
# stty ixoff -ixon
### If needing to listen to Ctrl-S for some apps, use these two instead:
stty stop undef
stty start undef

Open your .bash_profile and put:

stty -ixon

The value -xion doen't work for me. You can see the man entry: man stty.