Keywords and reserved words: What's a poor boy to do? We have been using MySQL since its beginnings. Back then we thought that descriptive column names were a good idea. So we created columns like date, open, high, low, close, volume, signal and so on that reflected the terms we actually used in our work. Some of which were keywords or reserved words and some of which became reserved words, like signal. As the years rolled by many programs in a wide variety of languages were written to use those tables. I gather you can see where this is going. In the step up from 5.0 to 5.5 MySQL included signal as a reserved word, which effectively means that we can no longer upgrade as many programs access the column signal and recoding would be a HUGE effort. We'd really like to upgrade and, now that Oracle has its hands on MySQL, we would also like to consider a move to MariaDB. So, what's a poor boy to do? Any thoughts/ideas greatly appreciated.
The best answer is what @akuzminksy mentioned: escape the fields.
Since you indicate doing so would be prohibitive in terms of amount of work required, there might be another solution: a pre-parse query rewrite plugin

A preparse query rewrite plugin has these characteristics:

The plugin enables rewriting of SQL statements arriving at the server before the server processes them.

The plugin receives a statement string and may return a different string.



Of course, that requires upgrading to 5.7! And the effort required to build this custom plugin might also be prohibitive.
Other tools that offer query rewriting capabilities are:

ProxySQL
MaxScale
ScaleArc

Since these tools are proxies, all rewriting is done 'preparse'.
Disclaimer: I make no claims that this will actually work, but is the only path forward I see besides code overhaul.