The men were located on Thursday on the remote Pacific island of Fanadik in Micronesia.
US Navy officials said they had been stranded for three days.
The crew aboard a US Navy plane, dispatched after the men were reported missing, spotted them around two hours into their search.
As well as the sign, the men were waving brightly-coloured lifejackets to attract attention.
The men said their vessel capsized due to a large wave a few hours after their departure from Pulap in the Federated States of Micronesia on Monday.
They say they spent the night swimming until they arrived on the island.
"Our combined efforts coupled with the willingness of many different resources to come together and help, led to the successful rescue of these three men in a very remote part of the Pacific," said Lt William White.
Three sailors have been rescued from an uninhabited Pacific island by the US Navy after spelling out "help" with palm fronds.