You have a requirement for users within your company to be able to manually choose from a selection of signatures.
This can be resolved through the use of Client-side signature application to let the user select the signature to be applied when they're composing the message.
For more information on client-side signature deployment, please see:
Once a client-side signature has been successfully deployed, the user will be able to select the required signature from the Signature dropdown menu within Outlook when composing a message:
They will then be able to see a list of signatures as they are named in the Exclaimer Cloud Portal.