Hook: Floor Medium Narrow (Blue Rectangle)The Flag: Rotworm Banner decoration fits into a narrow blue medium rectangle floor hook.
Hook: Floor Medium (Blue Square)The Flag: Rotworm Banner decoration fits into a blue medium square floor hook.
How to Get a Flag: Rotworm Banner Decoration
Credit Decorations (previously warzone decorations)
The Flag: Rotworm Banner decoration can be bought for 10,000 credits. It can be bought from a vendor in a room with a guild bank in the Crafting & Strongholds section of the fleet, NOT in the PvP section of the fleet. It does not require any special skills or PvP to acquire, just credits.
This item can be bought and sold on the GTN - beware of scammers and don't buy it from the GTN unless it is less than 10,000 Credits.
The Flag: Rotworm Banner decoration used to cost 1,000 Ranked Warzone Commendations + 1,000 Warzone Commendations, but Warzone Commendations were removed from the game so now it just costs 10,000 Credits.