install-signal-on-debian-buster.sh

#!/bin/bash

set -xe

############################################################
# First, installs an empty package that fulfills libappindicator1.equivs
# allowing signal linux to be installed on debian buster
############################################################

sudo apt install equivs

# Create a libappindicator1.equivs
cat > $libappindicator1.equivs <<- EOM
Package: libappindicator1
Version: 99:99
Maintainer: Nobody
Architecture: all
Description: dummy libappindicator1 to allow signal to install
EOM

equivs-build libappindicator1.equivs
sudo dpkg -i libappindicator1_99_all.deb

############################################################
# OK, now we'll run signal's deb install script:
############################################################

# 1. Install our official public software signing key
wget -O- https://updates.signal.org/desktop/apt/keys.asc |\
  sudo apt-key add -

# 2. Add our repository to your list of repositories
echo "deb [arch=amd64] https://updates.signal.org/desktop/apt xenial main" |\
  sudo tee -a /etc/apt/sources.list.d/signal-xenial.list

# 3. Update your package database and install signal
sudo apt update && sudo apt install signal-desktop

Are you sure about the dollar sign at line 13?

@hiqua how'd that get in there?!? JOY

Fortunately, no longer should be required, since it sounds like this is fixed properly upstream by using on libayatana-appindicator to fulfill the libappindicator requirement https://packages.debian.org/source/sid/libayatana-appindicator