The engraving route, and which machines can do it
The QuickSwap engraving tip scratches a line into a surface rather than frosting it with acid, and it fits the Maker and Maker 3 only. Explore machines and the Joy have no adaptive tool housing, so they cannot take it, whatever a Pinterest pin claims. Fine on anodised aluminium, soft metals, acrylic and leather; it will not engrave glass, and trying skates the tip across the surface.
An engraved design is a drawn path, not a filled shape, which changes how you build the file: the tip follows the outline of what you give it, so a solid filled letter engraves as its outline only. For a filled look, hatch it — a set of closely spaced parallel lines inside the shape, assigned to the engrave operation.
Mirror only when you are etching the far side
Etching the outside of a glass, which is the normal case, needs no mirroring at all. Mirror only if you are putting the stencil on the inside of a window or the back face of a clear blank so the design reads correctly through the glass.
This is the opposite default to iron-on, where mirroring is always required, and mixing the two up is how a name ends up backwards on a wedding gift.
What will not etch
Borosilicate glass — most Pyrex, a lot of lab-style glassware and many double-walled tumblers — barely reacts to etching cream. So does anything with a coating, which covers most powder-coated and painted tumblers. Test on the base before committing to a set of twelve.
Etching cream contains ammonium bifluoride. It is not a craft paste: wear nitrile gloves and eye protection, work with ventilation, keep it off skin, and follow the bottle for disposal. This is the one material in crafting where the label is worth reading in full.
Preparing the file here
Stencil work is mostly offset work, and the studio does both directions: an outward offset to fatten strokes until they survive the cream, and a contour offset to add a cut-out frame around the design so you have a margin of vinyl to burnish against.
Assign the design to the cut operation and export SVG for Design Space, or export DXF if you are stencilling from Silhouette Studio Basic. For an engraved piece, put the hatch lines on their own layer with the engrave operation so they arrive as a separate, correctly-mapped tool rather than merged into the cut.