It sounds to me like one of two possible cases. You are either too high level or playing through the game in hollow mode.
You can only see signs on the floor in human form. So make sure you are doing so. I see signs all the time. You may want to make sure you aren't playing in offline mode too.
You may want to change servers as well if none of the above is your issue. quitting the game and reloading it will log you into a new server.
If you want a better chance at PVP, the cat covenant in the forest offers pvp, the ring it gives you when equipped you can be called to the forest from any location (not a boss spot), when done you pop back up exactly where you left off. Anor Londo also features a PVP covenant as well. With the dark moon seance ring equipped enter the bonfire area below the turning platform, you also get a ring to be summoned just like the forest.
To see someones call sign they must be within 10% of your level adjust. Meaning if you lvl 50 you can summon only lvl 45-55