From Speedcoin [SPD] announcement above -

P.S. We made our Speedcoin [SPD] pre-announcement in March 2014 when no forks with a 'Speedcoin' name existed and
no other pre-announcement of a Speedcoin existed. On middle of April 2014 someone with another fork announced the same name 'Speedcoin'
but with a different unit name -  'SPC', Speedcoin [SPC].  Because a lot of work has already been done on our fork and since we made our pre-announcement earlier with a different unit name 'SPD', we have kept the our fork name as before which is Speedcoin [SPD].

Read here - https://bitcointalk.org/index.php?topic=579141.msg6370629#msg6370629