rpmsign: 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 CentOS possible default full paths are:

/usr/bin/rpmsign - from package: rpm

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/rpmsign - from package: rpm

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

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