I had a recollection of something I once learned for a litigation matter, that may be able to be used to help with marking hand pollinated flowers.

Most of the large banana producers use a system of marking buds. If a bud first appears during a given week, it receives a band or ribbon in a given color. Each bud banded during that week gets the same color. Buds need to be picked during a certain range of weeks, in order to make sure that they will not become overripe during transport to their markets. Each area has a different range, and the range can change with the seasons, but without the process, the bananas all end up becoming yellow too fast.

If a banana reachs a climacteric phase, there is no stopping it from ripening and it is also going to release a bunch of ehtylene gas which will trigger the start of the climacteric phase on all of the neighboring bananas. One climacteric banana can spoil the whole bunch.

Why not use a ribbon or band to mark any plant or fruit or whatever that you think needs marking in your garden?