
1) Armada Music artist 2) Biannual magazine 3) Dutch musical duo 4) German literary magazine
Found on
https://www.crosswordclues.com/clue/signum

Latin, meaning: sign, seal, indication, sign/ mark / token.
Found on
http://archives.nd.edu/sss.htm
[magazine] ``Signum: Blätter für Literatur und Kritik is a biannual literary magazine published in Dresden. The editor-in-chief is Norbert Weiss. He established the journal in 1999. Each issue is around 140 pages long and includes lyrical poetry, prose, drama, essays and reviews. A regular feature, Exkurs, provides information about work ...
Found on
http://en.wikipedia.org/wiki/Signum_(magazine)

function of a real variable equal to -1 for all negative values of the variable, +1 for all positive values and 0 for the zero value
Found on
http://www.electropedia.org/iev/iev.nsf/display?openform&ievref=101-13-05

A - standard. B - identification tattoo worn by soldiers.
Found on
http://www.encyclo.co.uk/local/20764

The standard of each century was called a signum. There were 2 variations of poles, one with a spear point and one with an open hand (manus) at the top. There were also circular disks attached, which identified the century and the cohort to which it belonged. The soldier carrying it was called a signifer. They were also used to identify turma. Also…...
Found on
http://www.encyclo.co.uk/visitor-contributions.php

sign, seal, indication, sign.
Found on
https://www.math.ubc.ca/~cass/frivs/latin/latin-dict-full.html
No exact match found.