Whether a port is Firewalled or just not opened

[Boryan Yotov]

Hello, everybody. I'm newbie at the firewall area :) so this question could sound a litle bit silly.   I would like to ask you if there is a way to understand whether a port on a remote machine is firewalled or just not opened. I use iptables to setup a firewall and I set a ACCEPT target for TCP port 80 for all "trusted" connections. All other connections to this port are DROP-ed (the INPUT chain policy is set to DROP).I'm currious whether someone could detect that the port is existing but firewalled e.g. available just for a few hosts.