External (or Remote) Container storage is not a document mgmt feature, but strictly a way for FMS to manage the data. So having another application touch those files is not a good idea.
Also: very carefully read chapter 9 of the FileMaker Training Series Advanced book; it lists all the gotcha's of trying to turn FM in nothing but a UI/scripting environment with an ESS database backend.
One alternative you can consider is to transform the captured signature into Base64-encoded text and store that into MySQL.
Thank you for your valuable insight. Will defiantly give it a read. In all honesty the reason I was planning to go for a external database is to better manage the stability of the database as it grows. Since I'm new to the product does query performance degrade as the database grows. I envision that around 500 - 1000 entries will be added to a particular table per month. Signatures are not really required for reporting purposes so they will be excluded from the eventual SQL statements.
With that few entries per month (up to 12,000 records per year) you will actually degrading performance by storing it in MySQL. The FileMaker db engine is more than capable of handling large numbers of records.
Your slowdown will come in the translation of the FM actions back to MySQL. Not by storing a few hundred thousand records in FM itself.
Thanks much appreciated, full FM solution it is