A rebus as compared to a palindrome is a little more difficult to decipher. In addition, the length of a rebus can be unlimited. Whereas the palindrome sentence becomes a bit non-sensical if too long .
Included with the Pioneer 10 and 11 space probes, that were launched in 1972 and 1973 respectively, plaques that depict the origins of the craft. The images transcribed thereon are pictograms and hopefully in many years will be deciphered by somebody or something.
With the subsequent Voyager probes, the plaques, which had transformed to golden discs, became a bit more eclectic. Enclosing the records is a cover with etched instructions, in form of a pictogram, on how to view and listen to its contents.
If one examines the the golden cover plaque, a Rosetta stone is needed to decipher how to read the analog phonograph records. I guess that Carl Sagan was correct when he noted, "The spacecraft will be encountered and the record played only if there are advanced space-faring civilizations in interstellar space". The readers of the records would have to be advanced since almost everything on Earth is now digitally based.