From: Smith, Gibbs M. Joe Hill Salt Lake City, Peregrine Smith Books, 1984 (which I highly recommend):
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[p.188]

    The day after the funeral, the I.W.W. committee in charge of the
arrangements returned to Graceland Cemetery to witness the cremation.
The body was photographed and identified for the last time on the
morning of November 26, then the casket was put on a slab of
stone and pushed into a blast furnace. Chaplin* relates:

       "Through a small hole in the side of the furnace, each
committeeman viewed the flame-lashed casket containing
the fine body and placid features of Joe Hill, dreamer, poet,
artist, and agitator, which had four purple bullet holes in
his young chest as punishment for the crime of being
"true blue" to his class-and to himself."

      Hill's ashes were placed in envelopes and distributed to
I.W.W. locals in every state but Utah. Envelopes were also
sent to South America, Europe, Asia, South Africa, New
Zealand, and Australia. On May 1, 1916, according to
Chaplin, the ashes were released to the wind.
Joe Hill's last will was fulfilled….

Printed on the envelopes that contained the ashes was the following:

FELLOW WORKER:
       In compliance with the last will of Joe Hill, his body was cremated at Graceland Cemetery, Chicago, Illinois, Nov. 26, 1915. It was his request that his ashes be distributed.
       This package has been confined to your care for the fulfillment of this last will.
       You will kindly address a letter to Wm. D. Haywood, Room 307,
164 W. Washington St., Chicago, Ill., telling the circumstances and
where the ashes were distributed.

WE NEVER FORGET

JOE HILL MEMORIAL COMMITTEE
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* Chaplin, Ralph. "Joe Hill's Funeral in Chicago" Solidarity 4 Dec 1915, p.1

The foregoing material can be found in the Labadie Collection at the
University of Michigan or in Joyce L. Kornbluh, ed., Rebel Voices:
An I. W. W. Anthology (Ann Arbor, Michigan: University of
Michigan Press, 1964), pp. 156-57.