Did the Ukrainian army put Wehrmacht crosses on the howitzers donated to them by the Czech government? No that's not true: The crosses used by the Ukrainian military are not Nazi symbols, but refer to the Order of the "Iron Cross" which was an award dating back to the Ukrainian War of Independence from 1917-1921.
The claim appeared in a video (archived here) on TikTok where it was published by @milanrostejnsky on May 18, 2023, with the title "#houfnice Dana in UA". It opened:
Czech howitzer Dana in Ukraine. This is what we all paid for...hopefully we wont pay for a retaliation..."
This is what the post looked like on TikTok at the time of writing:
(Source: TikTok screenshot taken on Mon May 22 13:09:47 2023 UTC)
The misinformation trend originated from a news report aired by Czech Television, showing how the Ukrainian army used the newly donated howitzer artillery cannons. The Dana artillery vehicles had visible white crosses on them, used for distinction. These have been mistaken for the Balkenkreuz used by the Nazi Wehrmacht army during WW2.
This misinformation spread across social media.