Books that are simply signed by the author are always desired by the serious book collector.
In the case of "The Adventurous Bowmen", the book was printed in 1926 and Pope (a medical doctor) died of phenomena on the morning of August 8, of that year. Obviously, Pope did not live long enough after the book was published to sign many copies of the book. So naturally there are only a handful of autographed copies of this book known.
The particular "The Adventurous Bowmen" that you ask about is inscribed to his surgical nurse, who was certainly a noteworthy person in Pope's world. Incidentally, she also was also Ishi's nurse before his death in 1916...
Pope inscribed in his distinctive printed hand, "To Helena Jorgensen who has been a surgical nurse & helped me so many ways - though not in shooting lions - Saxton Pope July 20, 1926"
Pope inscribed this book on July 20, 1926, he died a short 19 days later, on the morning of August 8, 1926.
Undoubtedly, this is one of the final copies of "The Adventurous Bowmen" that Pope inscribed before his death.