signify: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/signify - from package: signify

You may install the required package with command apt-get install {package}

Error in other languages:
signify: bevel nie gevind nie
signify: comandă negăsită
signify: comando não encontrado
signify: commande introuvable
signify: command not found
signify: käsku ei ole
signify: không tìm thấy lệnh
signify: komanda nerasta
signify: Kommando nicht gefunden.
signify: kommandot finns inte
signify: komut yok
signify: nie znaleziono polecenia
signify: níor aimsíodh an t-ordú
signify: no se encontró la orden
signify: no s'ha trobat l'ordre
signify: opdracht niet gevonden
signify: parancs nem található
signify: perintah tidak ditemukan
signify: príkaz nenájdený
signify: příkaz nenalezen
signify: команда не найдена
signify: командата не е открита
signify: 命令找不到
signify: コマンドが見つかりません