No Landing Sign / Prohibited Landing Marker / Helideck X Marker For certain operational or technical reasons, a Helicopterdeck may have to prohibit helicopter operations. In such circumstances, where the helideck cannot be used, the ‘closed’ state of the helideck shall be indicated by the use of a prohibited landing marker. The size of our marker has been tailored in size to cover the letter 'H' within the touchdown and positioning markers. The prohibited landing marker set is standard supplied with a storage bag and eight (8) tie-down straps.