Window representing the Son.
Window representing the Holy Spirit.
The front of the church has one window for each of the Persons of the Trinity: The Father (right), The Son (left), and The Holy Spirit (above). Two of the windows on the front of the church are not easily seen on the inside. The top of the "God the Father" window can only be seen by looking down from the choir loft. The bottom can be seen in the sacristy. The "God the Son" window can be seen in the lower and upper parts of the staircase to the choir loft. The "Spirit" window can easily be seen in the choir loft.

The IHS is an ancient symbol for Jesus. It uses the first two and last letters of the Greek word for Jesus - IHCOYC (the Y actually being a lambda and the C a sigma which becomes S in the latin alphabet). A horizontal line over the letters would be a sign that it was an abbreviation. Here the line is stylized into a crown, symbol of Christ's kingship.
OUTSIDE FRONT
Top of Trinity Father window
Bottom of Trinity Son window Bottom of Trinity Son window