/setblock ~ ~1 ~ standing_sign 0 replace {Text1:"{\"text\":\"Click here\",\"color\":\"red\",\"bold\":\"true\",\"clickEvent\":{\"action\":\"run_command\",\"value\":\"blockdata ~ ~-1 ~ {Command:/give @a minecraft:leather_helmet 1 0 {display:{Name:\\\"\u00A7fKnockback-Proof Helmet\\\"},Unbreakable:1,HideFlags:4,AttributeModifiers:[{AttributeName:\\\"generic.knockbackResistance\\\",Name:\\\"generic.knockbackResistance\\\",Amount:1.0,Operation:0,UUIDMost:82256,UUIDLeast:138937}]}}\"}}",Text2:"{\"text\":\"\",\"clickEvent\":{\"action\":\"run_command\",\"value\":\"setblock ~ ~ ~ minecraft:air\"}}"}